School Science Lessons
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5.0.0 Understanding Plants

Table of contents


5.01 Plant body

5.08 Stems

5.07 Leaves

5.11 Flowers

5.12 Flowers & fruits

5.13 Fruits

5.14 Bean seed

5.15 Bean germination

5.16 Planting material

5.24 Crop care

16.9.0 Seed sterilization

5.22 Pests & diseases
5.20 Insect pests

5.20.1 White fly

5.25 Plant ash

16.8.8 Corn smut

16.8.9 Head smut

5.19 Soil acidity

5.21 Plant diseases

5.02 Photosynthesis

5.03 Photosynthesis

5.04 Photosynthesis

5.09 Roots

5.10 Root hairs

5.10.01 Rhizosphere

The aim of this set of agriculture teaching notes is to teach students how food plants work and the reasons for the methods used to
care for crops in the school gardens.
These teaching notes will also help students to understand the other agriculture teaching notes that deal with crop projects.

5.01 Plant body
See diagram 9.53: Parts of a plant
You will need some small plants that have flowers, branches and roots.
Bring them to the classroom.
Give one plant to each pair of students.
Point to the parts of the plant body.
The plant body consists of two parts:
The shoot above the ground, and the root below the ground.
The shoot is the stem with the leaves.
The stem is divided by thick parts called nodes.
Leaves grow from the nodes.
Roots may grow from nodes when the nodes touch the wet ground, e.g. sugar cane or para grass.
Roots grow at the root tips.
A bud is a baby shoot.
The terminal bud is at the end of the shoot and either makes the shoot grow or forms a flower.
The axillary buds grow from the nodes.
They grow in the angle (axil) between the leaf and the stem.
Axillary buds can grow to form lateral shoots called branches.
The buds at the ends of the branches can either make the branch grow or form a flower.
Axillary buds make the plant grow short and bushy or they can form flowers.
Leaves make food in the sunlight using air and water.
The stem carries food and water between the leaves and the roots.
The stem holds up the leaves, and may store food, e.g. sugar cane.
Roots take in water and plant nutrients from the soil.
Roots hold the plant in the ground and may store food, e.g. sweet potato.
Plant nutrients are chemicals the plants need.
Flowers can form fruits containing seed.
The seeds can grow to form new plants.

5.02 Photosynthesis, light is needed for photosynthesis
All food comes originally from green leaves in the sunlight.
A process is a change in something, or a way in which something is made.
So you can say that photosynthesis is the process by which green plants make food.
Show the students the prepared demonstrations.
Where does all your food come from? [Green plants in the sunlight.]
In sunlight green, plants use carbon dioxide gas from the air, water, and plant nutrients from the soil to make food.
This process is called photosynthesis.
("Photo" means light, "synthesis" means putting together).
Plant nutrients are chemicals in the soil that plants need, e.g. plant nutrients are needed to make the green colour that absorbs the
sunlight energy.
This energy remains stored in the food.
The first food made in green plants is the simple sugar, glucose.
Photosynthesis equation
Carbon dioxide gas + water + sunlight energy --> simple sugar (food) + oxygen gas.
The oxygen gas produced by photosynthesis goes out into the air.
All your food comes originally from photosynthesis in a green plant because your food is either plants, or animals that have eaten plants.
Animals breathe in oxygen gas and breathe out carbon dioxide gas that is a waste.
Plants use the carbon dioxide gas during photosynthesis and give out oxygen gas.
To make food crops grow well they need:
1. Sunlight, but baby plants need some shade,
2. Water, but soil must not be waterlogged (filled with water)
3. Plant nutrients, but they must be the kinds of chemicals the plants need,
4. Green leaves.
The leaves must not be damaged by insects or disease, and they must not turn brown or yellow.

5.03 Photosynthesis, sunlight is necessary for photosynthesis
See diagram 9.145.1: Aluminium foil on leaf
Three days before the lesson fold a piece of aluminium foil to form a band around a leaf on a tree growing in the sunlight.
After three days, pick the leaf off the tree and remove the aluminium foil.
Drop the leaf in boiling water to kill it.
Put the leaf in methylated spirit to remove the green substance called chlorophyll.
Place the leaf in an iodine solution.
The part of the leaf not covered by the silver paper turns blue black colour.
The part of the leaf covered by the silver paper does not turn blue black because there was no sunlight for photosynthesis to make
Students could form their own initials out of silver paper and "write" them on a leaf.
Do the last part of the demonstration in front of the students.
The simple sugars produced by photosynthesis are soon changed to starch in the leaf.
When iodine solution is added to starch it changes from a white colour to a blue black colour.
A leaf with a silver paper band around it is left on a tree for three days.
The leaf is then picked and tested for starch.
The part of the leaf shaded by the silver paper shows no starch present.
The part of the leaf not shaded shows starch.
Conclusion: Sunlight is necessary for photosynthesis.

5.04 Photosynthesis, oxygen gas is formed during photosynthesis
See diagram 9.145.1: Waterweed in the light and in the dark
Demonstration: Oxygen gas is given off during photosynthesis
Try out the demonstration a few days before the lesson.
The demonstration works best if you can start it the day before the lesson.
start the demonstration at the beginning of the lesson and allow students to see it again in the next lesson.
A suitable waterweed is Elodea.
The demonstration works better if you add some sodium bicarbonate (baking soda) to the water.
Tests for oxygen gas
Light a thin piece of wood then blow out the flame leaving the wood glowing red.
f you put this into oxygen, the glowing wood will burst into flame.
Show the students the demonstration.
Put green waterweed in a test-tube and invert it under water.
The test-tube contains no air or bubbles in it.
This is left in the sunlight.
Another piece of waterweed is placed under a similar test-tube.
This is left in the dark.
After some hours, look at the waterweeds again.
The waterweed in the light has bubbles of oxygen gas coming from it.
No bubbles of oxygen gas come from the waterweed in the dark.
The gas was oxygen because it made a glowing piece of wood burst into flames.
Conclusion: During photosynthesis oxygen gas is given off.

5.07 Leaves
See diagram 9.66.2: Shapes of leaves
Collect samples of leaves with different shapes.
Some leaves should be the leaves of your crops.
Show the students the leaves you have collected.
Leaves are usually flat and thin so that they can catch plenty of sunlight and have little holes in the lower side to let gases and water
vapour move in and out.
The bushy plant the leaf has three parts: 1. leaf, 2. petiole, and 3. leaf blade.
The grass leaf has three parts: 1. leaf blade, 2. leaf sheath, and 3. ligule.
Draw the leaves of the different crop plants you are growing and describe their shape.

5.08 Stems
| See diagram 9.57.2: Section of cut wood
See diagram 9.57.1: Wood sections
The day before the lesson, stand a young plant in a jar containing enough red or blue ink to cover the roots.
Find a stump of a tree or coconut that has been cut down recently.
Get a piece of sugar cane, a yam, a taro corm, a bit of banana corm and a ginger or tumeric rhizome.
You will need a razor blade for this lesson.
Show the students the young plant standing with roots in red ink.
Take the plant out and wash it.
Then cut the stem and open it with a razor blade to show the ink inside.
What does this prove? [Liquids move up the stem.]
Show the students the cut stump of a tree.
What is the function of the wood? [To let the plant become large and strong]
Eat some sugar cane.
What does this show? [Stems can be used to store food.]
Show the students the yam, taro and bit of banana corm.
Stems have three functions: transport of food from leaves to roots, transport of water and plant nutrients from roots to leaves,
support of leaves and branches.
In a young stem only a few leaves can be supported.
In a large tree many leaves and branches can be supported, food storage, e.g. sugar cane.
Table 5.08
Stem description
Swollen stem base
Swollen horizontal underground stem
Swollen rounded underground stem
Name of stem
stem tuber
banana, taro
ginger, tumeric

5.09 Roots
See diagram 9.73.1: Two main kinds of roots
Before the lesson, dig up a small bushy plant such as a mung bean and a grass such as para grass.
Wash the soil off the roots.
Show the students the bushy plant roots and grass roots.
1. Bushy plants have a main root called a tap root (or a primary root) and smaller lateral roots.
These roots grow very deep.
Grasses and palms have no main root, only many fibrous roots.
These are thin roots and do not grow deep.
2. Complete columns 2 and 3 of the Table 5.09.
Table 5.09
Kind of Root
Tuberous root
Aerial root
Prop roots
Swollen tap root
Stores food
Breathes above water
Holds up stem
Stores food
Sweet potato

5.10 Root Hairs
| See diagram 9.73.2: Root hairs 1
| See diagram 9.73.3: Root hairs 2
| See diagram 9.75: Root hairs 3
Remind the students of the need to transplant carefully so as not to damage the roots or root hairs.
Five days before the lesson put some bean seeds on wet paper or cotton wool on a plate.
Cover with a saucer or another plate to keep the seeds damp.
After germination, you will see small root hairs growing from the side of the root.
Use seed packaged in silver packets because they will be protected from attack by fungus.
Most plants take water and plant nutrients into their roots through tiny root hairs (but coconuts do not have root hairs).
The root hairs are very small, have thin walls and are easily damaged.
If plants do not get enough water the leaves will wilt then dry up and later the plant will die.
If you damage the root or root hairs during transplanting: insects or disease damage the root, e.g. bacterial wilt disease of tomatoes.
If there is not enough water in the soil, the soil water is salty.
If there is too much water in the soil you say that the soil is waterlogged.
Roots will die in waterlogged soil because they need some air to breathe.
Soils should be well-drained so that there is some air in them to give oxygen to the root hairs.

5.10.01 Root rhizosphere
The rhizosphere is the region just around the root hairs and fine roots that is influenced by root hair secretions and the local
In the rhizosphere the following processes may occur:
1. Excretion of H+ that exchanges for nutrient Mg2+, Ca2+, NH4+, K+.
2. Release of carbon dioxide from root hair cells by respiration.
3. Oxidation of nitrogen and sulfur to nitrate and sulfate ions.
4. Excretion of organic acids by the root hairs.
The organic acids may complex metals and increase the mobility of Al3+ and Fe3+.
5. Depletion of oxygen gas around the root hairs to reduce the redox potential and so favouring Fe2+ over Fe3+.
6. Removal of water by root uptake.
7. Change in soil permeability.

5.11 Flowers
See diagram 9.98.7: Flower parts and flowers
Before the lesson pick enough large flowers so there will be one flower for each pair of students.
Flowers to use
1. Poinciana Delonix) flower from a large tree, is a legume and forms large pods.
It has five sepals that are thick and green on the outside and red on the inside, five separate petals (The upper one is more showy.)
10 stamens, and an ovary like a bean pod.
2. Hibiscus flower is a large red flower with five sepals, five red petals, many stamens attached to a red tube separate from the style
that is inside it, five stigmas and so five female parts.
The flower does not usually produce seed.
3. Sweet Potato flower (Ipomoea) has five sepals joined, five petals joined to form a purple trumpet, five stamens attached to the
petals, and female part.
It can form little black seeds.
4. Other suitable flowers are tomato, chilli, wing beans, peanut.
Give the flowers to the students.
What are the shapes, colour and smells of the flowers?
Shake some pollen out of the flowers.
Most flowers contain male parts and female parts.
Insects are attracted to flowers by their shape, colour and smell.
They fly from flower to flower carrying pollen on their bodies and legs.
Pollen comes from the male parts.
Pollen makes the female part form a fruit and seeds.
This is called fertilization.

Hold the flower by the stalk and touch the following parts:
1. Receptacle: Where the stalk gets wider at the base of the flower.
It is a platform for the other flower parts.
2. Sepals: Like little green leaves on the outside of the flower.
They project the young flower in a flower bud.
3. Petals: Coloured parts inside the sepals.
They attract insects.
4. Stamens: The male parts.
Each stamen consists of a little stick called the filament that holds up a bag called the anther.
The anthers produce pollen.
Can you see the pollen coming out of the anthers?
5. Stigma: The top of the female part in the middle of the flower.
It is sticky and can catch the pollen.
6. Style: The long tube of the female part below the stigma.
Pollen can grow down inside the tube to fertilize the ovary.
7. Ovary: The swollen base of the female part that contains ovules.
After fertilization, the ovary will form a fruit and the ovules will form seeds.
Count the number of sepals, petals and stamens.
Then they should pull off some sepals and petals, and open the ovary to see the ovules.

5.11 Functions of the parts of flowers
| See diagram 9.98: Dicotyledon half flower
| See diagram 54.9.2: Chilli flower (dicotyledon)
| See diagram 9.98.1: Lily flower (monocotyledon)
For this lesson you will need chilli or tomato flowers, one for two students, and razor blades.
You will also need a chilli or tomato fruit.
Before the lesson, practice cutting a half flower.
To do this hold the flower upside down and cut down the middle of the stalk between two of the sepals and cut the flower in half.
Now check that the stigma, style and ovary are cut exactly in half.
You will need a magnifying glass to see all the ovules in the ovary.
Can you count them?
Give a flower to each pair of students.
Name each part of the flower as you point to them.
Show the students how to cut a half flower.
Touch each part of the half flower.
Students should also touch each part of their half flower and tell you is name and function:
6. Stalk
5. Receptacle: platform for other parts
Functions of flower parts
1. Sepals: protect flower bud
2. Petals: attract insects
4a. Stigma: female part, pollen sticks to it
4b. Style: pollen grows down it
4c. Ovary: pollen fertilizes it to form a fruit
7. Ovule: pollen fertilizes it to form seed
3b. Filament: part of male stamen, holds up anther part
3a. Anther: part of male stamen, produces pollen
8. Pollen: can fertilize the ovary and ovules to produce fruit and seed.
After fertilization, sepals, petals, stamens, stigma, and style usually die and fall off.

5.12 Flower and fruit formation
See diagram 9.4.2: Tomato flower and fruit formation
Collect some green tomatoes and tomato flowers, one of each for each group of four students.
You could also use chilli or eggplant (aubergine) fruit and flowers.
You will need some razor blades and a magnifying glass.
Examine the flowers and fruit, cut them down the middle with razor blades.
BE CAREFUL! Show them the ovary (fruit) and ovules (seed).
The remains of the sepals, petals, stamens, stigma, style, may be seen if they have not dropped off.
After pollen sticks to the stigma and grows down the style into the ovary, the ovary swells to form a fruit.
The ovules in the ovary become seeds.
Pollination is when the pollen touches the stigma and sticks to it.
Big flowers are pollinated by insects.
Small flowers such as grass are pollinated by the wind.
Fertilization is when the male pollen reaches the ovary and ovules.
The pollen grows down the style to the ovary.
Tell the students to draw their cut tomato flowers and fruit.
After fertilization, the flower stalk becomes the fruit stalk, the sepals, petals, stamens, stigma and style usually die, the ovary becomes
the fruit, the ovules become seed.

5.13 Fruit
| See diagram 9.100.3: Succulent fruit
| See diagram 9.100.4: Berry, drupe legume
| See diagram 9.100.5: Pome, apple
| See diagram 53.7: Coconut fruit
| See diagram 58.1: Papaya fruit
| See diagram 9.113.4: Maize kernel, caryopsis
Collect examples of the eight different kinds of fruit.
When preparing the lesson, use only examples of fruit that the students have seen.
Show the students the different examples of fruits you have collected.
A fruit is a swollen ovary with one or more seeds inside.
Kinds of fruit:
Caryopsis, "grain": single carpel so a single seed is tightly closed in the ovary wall, indehiscent, pericarp fused with thin seed coat,
e.g. maize, wheat.
Capsule: A dry fruit that opens to let the seeds out, e.g. cassava, sweet potato, okra.
Pod: A dry fruit that opens on two sides to let the seeds out, e.g. legume (cowpea, wing bean, peanut)
Berry: Fruit wall in two layers - outer layer is a tough skin, inner layer is thick and juicy, e.g. tomato, chilli, papaya, guava, banana.
Citrus fruit: Like a berry with thick peel and oil glands, e.g. orange, lime, pomelo.
Gourd: Like a berry with a hard outer skin, e.g. pumpkin, melon, snake gourd.
Drupe: Fruit walls in three layers: outer thin, middle thick, inner very hard - called a shell or stone, e.g. coconut, mango, coffee.
Multiple fruit: Many fruits stuck together to form one fruit, e.g. pineapple, breadfruit.

5.14 Bean seed
See diagram 9.113: Soaked bean seed
Two days before the lesson put some bean seeds in water.
Use enough seed for each student.
Also, have one dry bean seed ready for each student.
Leave the bean seeds in water in the classroom so the students can observe the seed coats swell and become wrinkled, then later
become smooth when the insides of the seed swells.
Give each student a dry bean seed.
See: the hard shiny seed coat, the scar where the seed was originally attached to the fruit, the tiny hole (micropyle) at the end of the
scar to let water and air in.
The baby root (radicle) grows out through this hole.
Give each student a bean seed soaked in water.
The soaked seed is larger and softer because water has gone through the tiny hole.
When the water goes into the seed coats, they are first wrinkled and later smooth when the whole seed swells.
Cut open the seed coat with a finger nail or razor blade and see the baby plant inside.
The two main parts in halves are the cotyledons swollen with stored food.
Between the cotyledons is the baby shoot (plumule) and the baby root (radicle).
Tell the students to draw their seeds or draw Diagram 16
Seed coats (outside), scar, hole (micropyle)
Baby plant (embryo)
Baby plant shoot (plumule)
Baby plant root (radicle)
Seed leaves (2 cotyledons) (store of food)

5.15 Germination
See diagram 9.113.2d: Bean seeds germinating
Two weeks before this plant 5-10 bean seeds at different levels as the diagram.
This can be done behind a piece of glass or in a glass aquarium, but keep the seeds in the dark.
Before the lesson, dig up germinated bean seeds at different stages of germination.
In the type of germination in the diagram, called epigeal germination, the cotyledons come out of the ground.
In the other type of germination, hypogeal germination, the cotyledons remain below the ground.
Show the students the seeds at different stages of germination.
Seeds are alive but they breathe very slowly.
When a seed is placed in the damp ground and water enters the hole the seed becomes very active, breathes more quickly and a new
plant starts to grow.
This is called germination.
The baby plant uses the stored food in the seed until it can produce green leaves and make its own food.
Stages in germination of a bean seed: The seed swells and the radicle (baby plant root) grows out the hole in the seed coat.
The stem below the cotyledons grows into a loop.
This stem straightens and the cotyledons and the first leaves are pushed up out of the ground.
Conditions for good germination are as follows:
1. Water,
2. Air to let the baby plant breathe,
3. Healthy seed,
4. Correct depth of planting,
5. Correct variety kind of seed for tropical countries
The problem of poor germination is usually caused by sowing seeds too deeply, or over-watering or under-watering.
If the seed is planted too deeply, the tiny developing plant exhausts the food supply in the endosperm long before the shoot and leaves
have broken through the soft surface and it dies.
The general rule is to plant a seed at a depth that equals twice its width.
Water newly-sown seeds with a mixture of one fifth of a teaspoon of Epsom salts in a litre of water to aid the germination process.
The magnesium in the salts will help stimulate the enzymes that make the food in the endosperm more readily available to the young
Small seeds should be only lightly covered with soil, but larger seeds will be planted at a greater depth.
The surface of the soil dries out more quickly than it does a few millimetres deeper.
So small seeds that are surface-sown should be kept moist while the larger seeds should be given a good soaking at planting time and
then watered again only after they break through the ground.
If you water the larger seeds too much, they will rot in the moist soil.
The seed of many vegetables and flowering annuals are F1 hybrids,
where the plant breeders have combined two different strains each with desirable characteristics.
However, F1 hybrids usually do not set seed or the seeds are not viable.
To select tomato seed for planting, squeeze the pulp and the seeds on absorbent paper, e.g. a paper towel, and spread it evenly
over the paper.
Remove as much pulp as possible and lay the remainder in the sun for two weeks to dry the germination inhibiting enzymes.
Lay the paper towel with seeds uppermost on seed raising mix and lightly cover with fine seed mix.
Water lightly until the seedlings emerge.

5.16 Planting material
| See diagram 9.81: Bulb
| See diagram 9.82: Corm
| See diagram 9.83: Rhizome
| See diagram 9.93.1: Stem cuttings
| See diagram 9.93.2: Cuttings
Collect examples of the different kinds of planting material to show the students in the classroom.
Find pictures of planting material mentioned in the lesson from your agricultural reference library.
Show the students the different kinds of planting material and the pictures from the agricultural reference library.
Planting material means seeds or parts of plants that can grow to become a new plant.
The parts of plants may be pieces of stems or special kinds of stems.
Seeds are produced in the ovary of a flower after pollen from the stamen (father) fertilizes the ovary (mother).
So seeds are like the children of the stamen and the ovary.
The pollen that fertilizes the ovary may come from the same flower as the ovary (self-pollination) or come from a different flower on a
different plant (cross-pollination).
The seeds (children) will have a mixture of the different characters of the parent plants.
So the seeds will be like brothers and sisters.
When they grow, they will all look like the
parents and like each other but none will look the same.
Plants that grow from parts of plants will grow to look the same as the parent plant.

Parts of plants used for planting material:
Stem cutting: When the nodes of some plant stems touch damp soil, they will produce roots.
If these stems are cut between the nodes then each node can form roots and shoot and grow into a new plant, e.g. sweet potato or
Stems or stem tips are cut and planted so that some nodes are under the ground and some are above the ground.
The nodes under the ground produce roots and the nodes above the ground produce leaves.
Corms area swollen stem bases, e.g. taro and banana.
The corm will have small buds growing from the nodes.
The corm can be cut into "bits", which are pieces of corm with buds.
Each "bit" can be planted to grow into a new plant.
Stem tubers are swollen stems or branches that grows in the ground, e.g. yams.
Each "eye" in the tuber is really a very small leaf and axillary bud.
The tubers can be cut into pieces, each containing an eye, and planted.
Each piece will grow into a new plant.
Root tubers cannot be used for planting material because there are no nodes or axillary buds in roots.
However, at the neck of the tuber where the root becomes stem axillary buds can sprout, be separated, and then used as planting
material, e.g. sweet potato or cassava.
Bulbs are shoots with fleshy leaves that store food, e.g. spring onion.
Some plants can produce little daughter bulbs that can be separated and planted to grow into big plants.
Shoots are from underground stems that produce shoots from their axillary buds.
They can be separated by cutting, then planted out, e.g. sword suckers of banana corms, tops and slips of pineapples.
Rhizomes are shoots that grows horizontally underground.
It can be easily broken into pieces, with each piece containing axillary buds.
The axillary buds can form new roots and shoots, e.g. ginger or tumeric, and many grasses.
Aerial suckers are branches which grow in the air than touch the ground.
Where a node touches the ground, a new plant can grow, e.g. pineapple aerial suckers, taro suckers, yam bulbils.

5.19 Acid & alkaline soils
See diagram 6.65.3: Nitrogen cycle
Soil pH is a measure of the acidity of the soil, on a scale from 1 to 14, the pH scale.
A neutral substance such as pure water has a value of 7.
Strong alkaline solutions have a pH near 14.
Strong acids, e.g. hydrochloric and sulfuric acid, have a pH value close to 1.
Most soils have a pH range of 4.0 to 9.5.
Most plants prefer a pH of between 5.5 and 7.5, with a pH of 6.2 to 6.5 ideal for most food plants.
It is desirable to keep the soil's pH in this range.
Incorrect soil pH affects the availability of many plant nutrients and so affects plant growth.
For example, phosphorus is an important nutrient for plant growth but if the pH drops below 5, the availability of
phosphorus sharply decreases because the phosphorus in the soil, present as phosphates, forms insoluble compounds at low pH,
stopping them from dissolving in water, so plants cannot absorb the phosphorus.
At low pH values many soil bacteria will not survive so changing the turnover rate in nutrient cycles, including the important nitrogen
The soil pH requirements of plants vary.
Some plants grow well under acidic conditions, while others grow best in a more alkaline soil; e.g. potatoes and watermelons like
slightly acidic soils, while apples and lucerne grow well in slightly alkaline soils.
Soil acidity increases through the removal of some basic nutrients from the soil, e.g. calcium leaching and the excessive use of fertilizers,
particularly nitrogen fertilizers.
To correct low soil pH, use application of lime (calcium compounds) or dolomite (calcium and magnesium compounds).
Use 1-5 tonnes / ha of lime to increase the pH of the topsoil to pH 6.5 but it can take several years to take effect.
You can improve the fertility of your garden soils by treating them so that they are not too acid or too alkaline.
Clay soils need a much greater amount of lime to shift the pH than sandy soils.
The pH scale measures whether substances are acid or alkaline.
pH 1 very strong acid that can burn you, e.g. battery acid
pH 6 weakly acid, e.g. soda water
pH 7 neutral, neither acid nor alkaline, e.g. water
pH 8 weakly alkaline, e.g. soap
pH 14 very strong alkali that can also burn you.
Acids have a sharp raw taste, e.g. unripe oranges or bush limes.
Alkalis have a slippery feel, e.g. soap, saliva.
Plants can absorb plant nutrients best when pH is 6 to 7.
In soils formed from coral rock the pH will be too high.
In swampy land the pH will be too low.
To lower the pH add rotten compost.
To raise the pH add lime.
In this lesson show how to use a "Soil pH Test Kit".
You will need: Coral soil or coral sand, well drained dark soil, swamp soil.
Plants cannot absorb plant nutrients from the soil if the soil is too acid or too alkaline.
Soils that are not well-drained are too acid.
Soils made from coral rocks are too alkaline.
You can test the soils using a colour test.
If the colour of soil in the test turns yellow orange, the soil is too acid.
If colour if soil in the test turns blue purple, the soil is too alkaline.
If colour if soil in the test turns dark green, the soil is not too acid nor too alkaline.
Collect just enough soil from just under the surface of the soil to cover your little finger nail, and place on a white plate.
Shake two drops of the indicator on the soil and mix to a paste with the stick.
Sprinkle some special white power on the paste.
Wait a few minutes then match the colour of the powder with the colour chart.
Do this for swampy soil, coral soil, dark well drained soil.
Acids have a sharp sour taste and can dissolve substances, e.g. in a car battery.
Alkalis have a slippery feel and can dissolve substances, e.g. soap.
Plants cannot absorb plant nutrients from the soil if the soil is too acid or too alkaline.
Soils in swampy ground are too acid for most plants.
Soils made from coral sand are too alkaline for most plants.
Make soil less acid by adding burnt shells hammered to a powder, and by draining the soil.
Make soil less alkaline by adding rotten plants from a compost heap.
Good soil is dark in colour from the rotten plants and is well drained.
To make sure that the soil is not too acid and not too alkaline the agriculture field officer can do a soil test.

5.20 Insect pests of plants
See diagram 9.303: Insect pests
Before starting to teach this and the next lesson, make a collection of pests and diseases from your garden.
They can usually be preserved in methylated spirits.
Also, collect diagrams of different pests.
make sure that your garden is a good example of pest and
disease control.
Check your spray equipment and pesticides.
A field visit may be useful for this lesson.
Show the students the examples of pests and diseases that you have collected from the garden.
To obtain the greatest possible production and cash income from your crops you must control loss by pests and diseases.
Pests are animals that eat your crops or infect your crop plants with diseases.
Pests may live in the ground, be attached to infected plants or may fly or walk to your crop.
Diseases are any change in the plant such as spots or holes in the leaves, wilting of the plant, rotting of the living plant.
They are caused by living things that may be so small that they cannot usually be seen by eye.
Diseases are carried by wind and water, infected plants, and pests.

The main pests of crops:
1. Nematode worms or eel worms: They are small worms pointed at both ends and have S-shapes.
They attack plant roots and may live in lumps on the roots.
They attack papayas, tomatoes, and bananas.
Killing nematodes or eel worms in the soil is very difficult.
2. Snails and slugs: Slugs are like snails with no shell.
They eat plant leaves and stems.
They can be controlled by picking off by students or by spraying with "Cuprox".
3. Spiders: Tiny red spiders called mites attack the leaves of beans and eggplant.
A chemical that kills them is called an acaricide, e.g. wettable sulfur.
4. Flies: Small white worms called larvae eat flowers and leaves, e.g. bean fly larvae.
5. Caterpillars: Some butterflies lay their eggs on the leaves and later caterpillars hatch out and eat the leaves.
They attack cabbages, tomatoes and beans.
6. Mole crickets and grasshoppers: They attack Chinese cabbage and lettuce.
7. Beetles: Beetles have hard shiny outer wings, e.g. Pumpkin beetle on pumpkins and sweet potato, Rhinoceros beetle on coconut
8. Bugs: Bugs have soft wings, e.g. vegetable bugs.
9. Rats: They eat root crops and fruit.
They can be controlled by destroying their nests and using poisonous bait, e.g. Warfarin.

5.20.1 Silverleaf white fly
Silverleaf white fly, sweet potato white fly, Bemisia tabaci, attacks sweet potato, tomato, cucumber, eggplant, poinsettia, okra, bean.
It sucks nutrients from phloem or lower leaf surfaces leaving chlorotic spots and withered leaves.
It produce a sticky substance, "honeydew", on which sooty moulds can grow, which reduce light to plant.
It is also vector for plant diseases, e.g. lettuce yellows virus, tomato yellow leaf curl virus, and African cassava mosaic, and cassava
brown streak virus.
There is no easy way to control it except by removing weeds near the crop.

5.21 Plant diseases
Before the lesson walk out in the garden and look for examples of infected plants to show the students.
Show the students different examples of plants infected by diseases.
When a disease attacks a plant you say the plant is infected with the disease.
The three main causes of disease in crops:
1. Fungus diseases: A fungus is like a plant with a body of threads, is not green, and can attack and digest green plants.
Many fungi live in the damp soil.
Chemicals that kill fungi are called fungicides, e.g. "Captan".
1.1 Damping off fungus disease: This fungus attacks germinating seeds and makes all the seedlings fall over and die.
It can be prevented by heating the soil to kill all the fungi before planting seeds.
This is called soil sterilization.
1.2 Collar rot fungus disease: It attacks the stem near the ground.
Leaf and stem fungus diseases.
There are many of these diseases.
They appear as yellow or brown spots that may later join, then the leaf or stem dies.
1.3 Powdery mildew: It looks like white threads on leaves or stems of pumpkins and cucumbers.
2. Bacterial diseases: Bacteria are tiny living things that are much too small to be seen.
They can attack plants and cause them to rot.
They live in damp places.
They cause many diseases, e.g. wilting of tomato plants, rotting of the heart of lettuce.
These diseases cannot usually be cured, but they can be prevented by soaking seeds in very hot water for a short time.
3. Virus diseases: Viruses are even smaller than bacteria and these diseases cannot be cured.
Viruses may cause yellow patches on leaves and later the plant dies, e.g. in taro and bananas.
These diseases cannot be cured but if the virus is carried by insects they may be controlled.
The best way to deal with bacterial or virus diseases is to burn the infected plant or part of the plant.
4. Diseases are carried to plants in four ways:
4.1 Wind can carry diseases a short distance.
4.2 Disease can be carried in running water or in the splash of rain drops.
4.3 Infected plants can pass disease to healthy plants if the plants are touching.
4.4 Disease can be carried by insect pests that can then infect healthy plan

5.22 Pests and diseases
In this lesson teach the students that you must be looking at your crops ever day for signs of pests and diseases.
Then you must be ready to decide what to do about the pests or diseases.
Often the pest or disease is harmless or does not do much damage so it is best to either leave it alone or just pick off insects or
diseased leaves by hand.
Yet you must still teach the students to look at the crops every day.
If the pest or disease is damaging your crop so much that you will not get enough to eat from it, or you cannot sell it, then be prepared
to use pesticide sprays or dusts: Contact the agricultural field officer and ask for advice.
Clean your spray pump and try it with water first.
Check that you have enough of the right kind of spray.
The only really safe pesticides to use in schools are as follows: Benomyl, Captan, Mancozeb, Maneb, Methoxychlor, Quintozene,
Sulfur, Zineb.
Mix the pesticide according to the instructions on the label.
Do the spraying yourself or supervise an older student very closely.
Keep the students away from the spray.
Do not spray on a windy day.
Wash your hands and face (using soap) after spraying.
Clean out the sprayer after use, do not leave any pesticide in the sprayer.
Store pesticides and chemicals in a safe place
away from students.
The teacher should show the correct way of spraying or dusting of pesticides in the garden
Show the students examples of good preparation.
Pests and diseases can be controlled by good preparation before you plant the crop.
Good management after you have planted the crop.
There are five methods of good preparation for control of pests and diseases.
Use healthy planting material.
Seeds and cuttings should be clean and free of insects or disease spots.
Imported seeds in sealed silver packets will be free of disease.
Select planting material and seeds from plants known to be resistant to disease.
In village gardens some kinds of yams resist disease and some are attacked by disease.
Prepare the land properly so the plants can grow well.
Dig the soil deeply and dig drains near by so the roots can grow strongly in the drained soil.
Fertilize the plants to provide enough plant nutrients.
Sick plants are damaged more by pests and diseases than healthy plants.
Dig out and burn all plants from the previous crop, weeds, and other stray plants, such as male papaya trees.
If you get rid of all unnecessary plants, then pests and diseases will not live on them ready to attack your crop.
Destruction of diseased or useless plants is called garden hygiene.
Soil for seed beds or seed boxes can be sterilized by heating the soil in an oil drum all day to kill pests and diseases.
The five methods of control are as follows:
1. Use healthy planting material
2. Select resistant planting material
3. Good land preparation
4. Garden hygiene
5. Sterilize soil for seed beds and boxes

5.24 Crop care
Show students some examples from your garden of: care of the crop, interplanting, need for control of pests and disease.
Show them how to control by hand.
Keep a record of their garden visits and observations in their note books.
Care of the crop: Keep soil cultivated between plants, well drained and free of weeds.
This will allow the crop to grow strongly and not lose any water and plant nutrients to weeds.
Use mulch to protect the soil but do not let it touch the plant stems because some disease may be in the mulch.
Add some compost or artificial fertilizer to provide plant nutrients to keep the crop healthy.
Interplanting can help plants to help each other so use a mixture of different kinds of plants in a garden, for example:
Table 5.24
Row 1
Row 2
Row 3
Row 4
sweet potato
sweet potato
climbing bean

If the same kinds of plants are separated from each other by other kinds of plants, it is harder for pests and disease to spread from one
plant to another.
Also some plants can help each other by shading weeds or repelling insects, e.g. marigolds will protect other plants from nematode
worms, radishes help other vegetables.
Control by hand: Insects such as caterpillars, diseased plants and parts of plants can be removed by hand and burnt.
Crops should be looked at every day for signs of pests and disease.
Garden hygiene: Do not leave diseased plants in the garden - pull them all out and burn them.
Also look at compost heaps and mulch for signs of insects that attack plants, e.g. Rhinoceros Beetle, mole crickets.
Control by spraying and dusting: Chemical sprays and dusts called pesticides can be used.
However, they are expensive and have to be handled with care because they are poisonous to people.
Use sprays or dusts only if it is essential, e.g. Carbaryl, Maldison, Dimethoate, Captan, Mancozeb, Acephate

5.25 Plant ash
| 6.65.1: Soil nutrients cycle 1
| 6.65.2: Soil nutrients cycle 2
| 6.65.3 Nitrogen cycle
Collect some white ash from burnt wood and bring it to the classroom.
The black ash is carbon.
Show the students the white ash you have collected.
Let them taste some.
It tastes a bit salty.
The ash contains plant nutrients.
Show the students a bag of fertilizer let them read the names written on the bag.
Do not let the students taste the fertilizer from the bags.
Plant nutrients are chemicals that plants take in from the soil.
Some people call them plant foods.
These chemicals are needed by the plant to keep it alive, to make food, and make the plant body.
If there are not enough plant nutrients in the soil, the plant will be weak, grow slowly, and have yellow or brown
It may die.
The most important plant nutrients are as follows:
1. Nitrogen for plenty of strong green leaves
2. Phosphorus for root growth and making fruit
3. Potash (potassium oxide) for healthy plants
Other important plant nutrients are as follows:
4. Sulfur and iron for green leaves
5. Magnesium and calcium for healthy plants
There are other plant nutrients needed in very small amounts, which may be important for some plants, e.g. manganese, boron.
Most plant nutrients originally come from the rocks that formed the soil.
Other plant nutrients in the soil have come from plants that have died then rotted in the soil.
If a soil does not have enough of any plant nutrient, e.g. potash, you say it is deficient in potash.

16.8.8 Corn smut
Corn smut is a fungus Ustilago maydis that causes smut disease in maize plants.
The disease is recognized by the appearance of white swellings on the stem, leaves and ears of the maize; the swellings contain black
spores that are carried by the wind to other plants when the white swellings break open.

16.8.9 Head smut
Head smut fungus is a disease of maize and sorghum, caused by the fungus, Sphacelotheca reiliana.
The heads of the affected plants have black powdery particles and are completely destroyed.
It occurs in USA and China where it is becoming an increasing problem because of climate change]

16.9.0 Seed sterilization
1. Sterilization procedures may be enhanced by:
1.1 Placing the material in a 70% ethyl alcohol solution prior to treatment with another disinfectant solution.
The use of a two-step (two-source) sterilization procedure has proven beneficial with certain species.
1.2 Using a wetting agent, e.g. "Tween 20", added to the disinfectants to reduce surface tension and allow better surface contact.
1.3 Conducting the sterilization process under vacuum.
This results in the removal of air bubbles and provides a more efficient sterilization process.
2. Orchid seeds are very small and contain little food reserves.
A single seed capsule contain 1, 500 - 3, 000, 000 seeds.
Sowing the seed in vitro makes it possible to germinate immature seed (green pods).
It is much easier to sterilize green capsules about two-thirds ripe than individual seeds after the capsule has split open.
For example, the time to maturity of Cymbidium is 10 months.
For green capsule sterilization, soak the capsule in a 100% bleach solution for 30 minutes.
Dip the capsule into 95% alcohol, and flame.
Under aseptic conditions, open the capsule and scrape out the seed.
Carefully layer the seed over the surface of the culture medium.
3. Dry seed sterilization
Collect seed and place in either a small flask or bottle, or place in a shortened pipette which has one end sealed with cotton.
Seal the other end of the pipette with cotton, once the seed has been placed in the pipette.
Prepare a solution containing 5-10% commercial bleach containing a few drops of "Tween 20".
Add the bleach solution to the flask, or draw up the solution into the pipette.
Swirl the flask containing the seed and bleach or repeatedly draw and aspirate the bleach solution in and out of the pipette.
Sterilize the seed for 5-10 minutes.
Remove the bleach solution and rinse the seed with sterile tissue culture grade water.
Transfer the seed to sterile culture medium.