Relevance of Biology to Agriculture – SS1 Biology Lesson Note (Second Term)

Biology is relevant to agriculture because agriculture is the growing of crops and rearing of animals, and these are living things that biology studies.

Behavioural objectives

By the end of the lesson, students should be able to:

1. state at least four ways in which biology helps agriculture;
2. state the four bases on which plants are classified;
3. describe the botanical classification of plants into thallophytes, bryophytes and tracheophytes;
4. classify plants agriculturally and give examples of each class;
5. classify plants by life cycle and by size, with examples;
6. explain the effects of bush burning, overgrazing, tillage, deforestation, fertiliser application and pesticide application on the ecological system.

How is biology relevant to agriculture?

Biology gives farmers the knowledge of living things that they need to produce more and better crops and livestock.

• Classification: it helps farmers to identify and group crops, weeds, pests and livestock.
• Crop and animal improvement: knowledge of reproduction and heredity helps in selecting and breeding better varieties and breeds.
• Pest and disease control: knowing the life cycles of pests and the causes of disease helps farmers to control them.
• Soil fertility: it explains the roles of soil organisms, such as decomposers and nitrogen-fixing bacteria in legume roots.
• Nutrition and health: it guides the feeding and care of crops and farm animals.
• Conservation: ecology shows how farming practices affect the environment and how to protect it.

Why are plants classified?

Plants are classified because they exist in many forms and types, and grouping them makes them easier to study and use.

There are four bases for classifying plants:

1. Botanical classification: based on structure, function and evolutionary trends.
2. Agricultural classification: based on the use and economic value of the plant.
3. Classification based on life cycle: based on how long the plant lives.
4. Classification based on size: based on the height and form of the plant.

What is botanical classification of plants?

Botanical classification is the grouping of plants according to their structures, functions and evolutionary trends.

• The plant kingdom is subdivided into divisions, classes, orders, families, genera and species.
• Plants are generally placed in three broad groups: thallophytes (A), bryophytes (B) and tracheophytes (C).
• Tracheophytes are grouped into pteridophytes (D) and spermatophytes (E).
• Spermatophytes are grouped into gymnosperms (F) and angiosperms (G).
• Angiosperms are subdivided into dicot (H) and monocot (I).

What are the groups of plants in botanical classification?

• Non-vascular plants: A and B have no xylem and phloem.
• Vascular plants: C has xylem and phloem to carry water and food.
• Seed plants: E bears seeds.
• Flowering plants proper: G bears flowers and its seeds are enclosed in fruits.

What is agricultural classification of plants?

Agricultural classification is the grouping of plants according to their use to man and their economic value.

It is based on three things:

1. The product obtained from the plants.
2. The parts of the plant that are useful.
3. The economic importance of the plants.

Plants are grouped agriculturally into the following classes:

• Crops and weeds: plants needed on the farm are crops, while unwanted plants are weeds.
• Food crops and cash crops: food crops are grown mainly for human consumption, e.g. maize and yam. Cash crops are grown mainly to earn money, e.g. cocoa and coffee.
• Root crops: plants which store mainly starch in edible underground stems or roots, e.g. yam and cassava.
• Cereal crops: monocotyledonous plants of the grass family whose grains are eaten, e.g. maize, millet, guinea corn, rice and wheat. They are rich in carbohydrates.
• Fruit crops: plants whose fruits are eaten, e.g. orange, mango, avocado pear and cashew. They are rich in vitamins, minerals and sugar.
• Vegetable crops: herbaceous plants whose leafy or other soft parts are eaten, e.g. spinach, lettuce, carrot, cabbage, okra, tomato, onion and pepper. They are rich in vitamins and minerals.
• Legumes: plants of the bean family whose seeds are eaten, e.g. cowpea and groundnut. They are rich in protein.
• Spices: plants whose parts are used to season food, e.g. pepper, curry, thyme and ginger.
• Latex plants: plants grown for latex (a milky fluid), e.g. rubber, used to make natural rubber.
• Fibre plants: plants that give fibre for textiles and bags, e.g. cotton and hemp.
• Beverage and drug plants: plants whose parts are taken as drinks, stimulants or medicine, e.g. tea, coffee, cocoa, kola nut and the quinine tree (medicine).
• Oil plants: plants that produce oil of economic value, e.g. oil palm, shea nut, groundnut, coconut, castor oil plant and melon.

How are plants classified by life cycle?

Classification by life cycle groups plants by the length of time they live, and there are three groups: annuals, biennials and perennials.

• Annuals: plants that complete their life cycle within one growing season or one year, e.g. maize, yam, melon, cowpea and tomato.
• Biennials: plants that complete their life cycle in two years, e.g. carrot, cabbage and onion.
• Perennials: plants that live for more than two years and yield every season, e.g. orange, mango, oil palm and cocoa.

How are plants classified by size?

Classification by size groups plants into three categories: herbs, shrubs and trees.

• Herbs: small plants with soft, fleshy stems, e.g. spinach and waterleaf.
• Shrubs: medium-sized plants with woody stems branching close to the ground, e.g. hibiscus.
• Trees: big plants with woody trunks that branch at the top, e.g. iroko, mahogany and cashew.

How do agricultural activities affect the ecological system?

Farming practices change the soil, the plants, the animals and the air of an area, and so affect its ecological system.

1. What is bush burning and what are its effects?

Bush burning is the setting of fire to the bush to clear vegetation.

• It destroys organic matter in the soil.
• It pollutes the air with smoke.
• It kills many soil micro-organisms.
• It exposes the soil to erosion and leaching.
• It reduces the water-holding capacity of the soil.
• It can lead to the extinction of some animals.
• The ash makes the soil slightly alkaline.

2. What is overgrazing and what are its effects?

Overgrazing is putting more animals on a pasture than it can support, which exceeds its carrying capacity.

• It removes the vegetative cover of the soil.
• It exposes the soil to erosion.
• It destroys the soil structure.
• It compacts the soil through continuous trampling.
• It causes poor growth and poor regeneration of vegetation.
• Possible benefit: animal droppings add nutrients that can improve soil fertility.

3. What is tillage and what are its effects?

Tillage is the working, digging or breaking up of the soil to prepare it for planting.

• Useful: it loosens the soil.
• Useful: it improves soil aeration.
• Harmful: it encourages leaching.
• Harmful: it exposes soil organisms and may kill some.
• Harmful: it changes the soil structure and texture, and so the ecology of the land.
• Harmful: intensive tillage can lead to loss of soil fertility.
• Harmful: it exposes the soil to erosion.

4. What is deforestation and what are its effects?

Deforestation is the continuous removal of trees, by bush burning or indiscriminate felling, without replacing them.

• It reduces water percolation, because humus and dead leaves are absent.
• It reduces rainfall in the area.
• It hinders the activities of soil micro-organisms.
• It causes loss of nutrients through leaching and erosion.
• It reduces the wildlife population.
• It reduces the humus content of the soil.

5. What is fertiliser application and what are its effects?

Fertiliser application is adding chemicals or other substances to the soil to improve its fertility.

• Useful: it supplements the nutrient content of the soil.
• Useful: it increases the productive capacity of the soil.
• Useful: it stimulates vegetative growth, which reduces soil erosion.
• Harmful: it can reduce organic matter or humus.
• Harmful: it can spoil the soil structure.
• Harmful: excessive use can cause soil acidity.

6. What are pesticides and herbicides and what are their effects?

Pesticides are chemicals used to kill pests, while herbicides are chemicals, as solutions or gases, used to kill weeds.

• Useful: they reduce the population of the target insects or weeds.
• Harmful: they pollute the environment.
• Harmful: they kill useful plants and animals.
• Harmful: they may leave undesirable residues in the environment.
• Harmful: when washed into rivers or lakes, they can kill aquatic animals.

Evaluation

1. State four ways in which biology helps agriculture.
2. State the four bases on which plants are classified and name the three broad botanical groups.
3. What are cereal crops? Give two examples.
4. Distinguish between annuals and perennials, giving one example of each.
5. State three effects of bush burning on the ecological system.

Assignment

1. Choose any three of the six farming practices in this note. For each one, define it and state two effects on the ecological system.