Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Relevance of Biology to Agriculture
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Relevance of Biology to Agriculture
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Subject: Biology
Class: Senior Secondary 1
Term: 3rd Term
Week: 2
Theme: The Organism And Its Environment
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Classify plants usingbotanical and agriculturaltechniques of classification. Describe the effects of various agriculturalactivities on ecologicalsystems. Identify pests of certain crops and in dicatetheir control. Describe somecommon diseases causedby pests and the ircontrol. Identify factors thataffect production of crops Identify some methods of preservingand storing foodstuff. List the factors that(i) affects populationgrowth (ii) affects the availability of man's food.
Plants are classified to organise them, understand their characteristics, and determine their uses. 2.1.
1. Botanical Classification (Scientific/Taxonomic Classification) This system groups plants based on their evolutionary relationships and structural characteristics.
The primary hierarchical ranks are: Kingdom: Plantae Phylum/Division: e.g., Magnoliophyta (flowering plants)
Class: e.g., Monocotyledoneae (monocots) or Dicotyledoneae (dicots)
Order: Family: Genus: Species: Key Classes relevant to agriculture: Monocotyledoneae (Monocots): Characterised by having one cotyledon in the embryo, parallel venation in leaves, fibrous root systems, and flower parts in multiples of three.
Examples in Nigeria: Maize (Zea mays), Rice (Oryza sativa), Millet (Pennisetum glaucum), Sorghum (Sorghum bicolor), Oil Palm (Elaeis guineensis).
Dicotyledoneae (Dicots): Characterised by having two cotyledons in the embryo, reticulate (net-like) venation in leaves, taproot systems, and flower parts in multiples of four or five.
Examples in Nigeria: Cassava (Manihot esculenta), Yam (Dioscorea spp.), Cowpea (Vigna unguiculata), Groundnut (Arachis hypogaea), Cocoa (Theobroma cacao), Mango (Mangifera indica). 2.1.
2. Agricultural Classification (Based on Use/Agronomic Purpose) This system classifies plants based on their economic or cultural use to humans.
Cereals (Grains): Cultivated for their edible starchy grains.
Examples: Maize, Rice, Millet, Sorghum, Wheat.
Legumes: Grown for their protein-rich seeds (pulses) or for their ability to fix nitrogen in the soil.
Examples: Cowpea, Groundnut, Soybean, Beans, Lentil.
Root and Tuber Crops: Cultivated for their underground storage organs rich in carbohydrates.
Examples: Yam, Cassava, Sweet potato, Cocoyam, Irish potato.
Fruits: Plants bearing fleshy, edible ovaries, usually sweet.
Examples: Orange, Mango, Pineapple, Banana, Pawpaw, Guava, Cocoa (pods are fruit).
Vegetables: Plants whose leaves, stems, flowers, or roots are eaten, usually savoury.
Examples: Fluted pumpkin (Ugu), Okra, Amaranth (Tete), Garden egg, Spinach, Cabbage.
Oil Crops: Grown for their oil-rich seeds or fruits.
Examples: Oil Palm, Groundnut, Soybean, Sesame, Melon seed.
Fibre Crops: Cultivated for fibres used in textiles, ropes, etc.
Examples: Cotton, Jute, Sisal.
Beverage Crops: Used to produce drinks.
Examples: Cocoa, Coffee, Tea.
Spices: Used for flavouring food.
Examples: Pepper, Ginger, Onion, Garlic.
Forage Crops: Grown as feed for livestock.
Examples: Various grasses and legumes (e.g., Gamba grass, Stylosanthes). Agricultural practices, while essential for food production, can have significant impacts on the environment.
Bush Burning (Controlled Burning): Description: Deliberate setting fire to vegetation, often done to clear land for planting, control weeds, or flush out game.
Effects: Soil Nutrient Loss: Destroys organic matter and nitrogen-fixing bacteria; volatilises nitrogen, sulphur, and phosphorus, reducing soil fertility.
Soil Erosion: Removes protective vegetation cover, exposing bare soil to wind and water erosion, especially during heavy rains.
Air Pollution: Releases greenhouse gases (CO2, methane) and particulate matter, contributing to climate change and respiratory problems.
Biodiversity Loss: Kills beneficial soil microorganisms, insects, small animals, and destroys plant seeds, reducing local biodiversity.
Habitat Destruction: Damages habitats for wildlife, forcing displacement or extinction.
Deforestation: Description: Clearing of forest land for agriculture, logging, or urban expansion.
Effects: Habitat loss, reduced biodiversity, increased soil erosion, altered rainfall patterns, increased atmospheric CO2, desertification.
Overgrazing: Description: Allowing livestock to graze excessively on pastureland, not giving vegetation enough time to recover.
Effects: Soil compaction, reduced vegetation cover, increased soil erosion, shift to less palatable plant species, desertification. Use of Agrochemicals (Pesticides, Herbicides, Fertilizers): Description: Application of synthetic chemicals to control pests/weeds or enhance soil fertility.
Effects: Water Pollution: Runoff into rivers, lakes, and groundwater contaminates water sources, harming aquatic life and potentially humans.
Soil Contamination: Accumulation of toxic residues, affecting soil organisms and crop quality.
Harm to Non-Target Species: Kills beneficial insects (e.g., pollinators, natural predators), birds, and other wildlife.
Biomagnification: Accumulation of toxins up the food chain.
Eutrophication (from fertilisers): Excessive nutrient enrichment in water bodies, leading to algal blooms and oxygen depletion, killing aquatic life.
Monoculture: Description: Growing a single crop species over a large area year after year.
Effects: Reduced biodiversity, increased susceptibility to specific pests and diseases, rapid depletion of specific soil nutrients.
Irrigation (Improper): Description: Artificial application of water to crops.
Effects: Waterlogging (drowning roots), salinization (accumulation of salts in topsoil), depletion of groundwater resources.
Tillage (Excessive): Description: Ploughing and turning over soil frequently.
Effects: Disruption of soil structure, increased soil erosion, loss of organic matter, destruction of soil microbial communities. 2.3.
1. Definition of Pests: Pests are any organisms that cause economic damage to crops, livestock, or agricultural products. They include insects, nematodes (roundworms), rodents, birds, and weeds. 2.3.
2. Common Pests in Nigeria and Their Effects: Insect Pests: Stem Borers (e.g., Busseola fusca in maize/sorghum): Larvae tunnel into stems, causing wilting, stunted growth, and reduced yield.
Maize Weevil (Sitophilus zeamais): Damages stored maize grains, creating holes and leading to significant post-harvest losses.
Cassava Mealybug (Phenacoccus manihoti): Sucks sap from young leaves and stems, causing stunted growth, leaf distortion, and reduced root yield. Aphids (e.g., on cowpea, vegetables): Suck sap, causing leaf curling, stunted growth, and vector viral diseases.
Locusts/Grasshoppers: Devastate entire fields by consuming leaves, stems, and fruits rapidly.
Yam Beetles (Heteroligus meles): Bore into yam tubers in the field, making them unmarketable and susceptible to rot.
Nematodes: Root-knot Nematodes (Meloidogyne spp.*): Microscopic worms that infect plant roots, causing galls (swellings), stunted growth, and reduced nutrient uptake (e.g., in cassava, yam, vegetables).
Rodents: Rats (Rattus spp.*): Eat stored grains, tubers, and growing crops in the field (e.g., maize, rice).
Birds: Quelea birds (Quelea quelea): Devastate cereal fields (rice, maize, millet, sorghum) during ripening.
Weeds: Striga (Witchweed, Striga hermonthica): A parasitic weed that attaches to roots of cereals (maize, sorghum, millet), drawing nutrients and severely stunting crop growth, causing "scorched earth" appearance.
Imperata cylindrica (Spear grass): A highly competitive and invasive grass that outcompetes crops for resources. 2.3.
3. Pest Control Methods: Cultural Control: Crop Rotation: Alternating crops (e.g., cereals with legumes) to break pest life cycles and improve soil health.
Mixed Cropping/Intercropping: Growing two or more crops together (e.g., maize and cowpea) can deter pests or attract their natural enemies.
Resistant Varieties: Planting crop varieties bred to naturally resist certain pests or diseases.
Timely Planting and Harvesting: Planting early or late to avoid peak pest populations.
Field Sanitation: Removing crop residues, weeds, and volunteer plants that can harbour pests.
Biological Control: Introduction of Natural Enemies: Using predators, parasites, or pathogens to control pest populations (e.g., Epidinocarsis lopezi wasp to control cassava mealybug in Nigeria).
Chemical Control: Pesticides: Using chemicals (insecticides, herbicides, nematicides) to kill or repel pests. Requires careful application, adherence to safety guidelines, and understanding of environmental impact.
Selective Pesticides: Targeting specific pests to minimise harm to non-target organisms.
Physical/Mechanical Control: Hand-picking: Manually removing large insect pests or weeds.
Traps: Pheromone traps, light traps, sticky traps for insects; live traps for rodents.
Netting/Fencing: Protecting crops from birds or larger animals.
Tillage: Ploughing to expose soil pests or bury weeds.
Integrated Pest Management (IPM): A holistic approach combining various control methods to manage pest populations below an economic injury level, while minimising environmental and health risks. It emphasises prevention, monitoring, and judicious use of interventions. While some diseases are directly caused by pathogens (fungi, bacteria, viruses), pests can play a crucial role as vectors or by creating entry points for pathogens. 2.4.
1. Pest-Vector Transmitted Diseases (Common in Nigeria): Cassava Mosaic Disease (CMD): Pathogen: Various species of Cassava Mosaic Virus.
Vector: Whiteflies (Bemisia tabaci).
Symptoms: Mottling, yellowing, distortion, and reduction in size of leaves. Stunted growth and significant yield loss.
Control: Planting resistant varieties (e.g., improved TMS varieties), using disease-free cuttings, rogueing (removing infected plants), controlling whitefly populations (though direct control is difficult on a large scale).
Maize Streak Virus (MSV): Pathogen: Maize Streak Virus.
Vector: Leafhoppers (Cicadulina triangula).
Symptoms: Characteristic yellow streaks on leaves, particularly prominent on young plants, leading to stunted growth and reduced grain yield.
Control: Planting resistant varieties (e.g., improved open-pollinated varieties), timely planting to avoid peak leafhopper populations, rogueing. 2.4.
2. Other Common Plant Diseases (Not always pest-vectored but important in Nigeria): Cocoa Black Pod Disease (Phytophthora palmivora): Pathogen: Fungus-like organism.
Symptoms: Brown to black lesions on cocoa pods, eventually covering the entire pod and rotting the beans inside. Affects leaves and stems too.
Control: Regular harvesting (early removal of ripe pods), pruning, field sanitation (burying infected pods), fungicide application, resistant varieties. Yam Anthracnose (Colletotrichum gloeosporioides): Pathogen: Fungus.
Symptoms: Dark lesions on leaves, stems, and petioles, leading to defoliation, dieback, and reduced tuber yield.
Control: Resistant varieties, fungicide application, good field hygiene.
Rice Blast (Magnaporthe oryzae): Pathogen: Fungus.
Symptoms: Diamond-shaped lesions on leaves, stems, and panicles, leading to reduced grain filling and significant yield losses.
Control: Resistant varieties, proper nutrient management (avoiding excessive nitrogen), fungicide application, timely planting. Bacterial Blight of Cassava (Xanthomonas axonopodis pv. manihotis): Pathogen: Bacterium.
Symptoms: Water-soaked spots on leaves that enlarge and turn angular, eventually leading to wilting, dieback, and defoliation.
Control: Using disease-free planting material, resistant varieties, sanitation (removing infected plants and crop residues). 2.4.
3. General Disease Control Principles: Exclusion: Preventing introduction of pathogens (e.g., quarantine, certified disease-free seeds).
Eradication: Eliminating pathogens from an infested area (e.g., rogueing, burning infected plants, soil sterilisation).
Protection: Shielding plants from pathogens (e.g., fungicides, resistant varieties).
Resistant Varieties: Breeding and planting crops with genetic resistance to specific diseases.
Cultural Practices: Crop rotation, proper spacing, balanced fertilisation, good field sanitation.
Food Security and Sustainable Agriculture: The knowledge gained in this topic directly applies to understanding the challenges of food security in Nigeria. Students can appreciate how biological principles (e.g., pest control, improved varieties, soil health) are vital for increasing food production and ensuring a stable food supply for a rapidly growing population. This fosters an understanding of sustainable farming practices (e.g., crop rotation, reduced bush burning) that protect the environment for future generations.
Career Opportunities in Agriculture: This lesson highlights various roles where biology intersects with agriculture, such as agricultural extension officers (advising farmers on pests, diseases, and crop management), food scientists (developing new preservation techniques), agronomists (optimising crop yields), and environmental scientists (assessing the impact of farming on ecosystems). This can inspire students to consider diverse career paths within the agricultural sector. Community-Level Decision Making and Environmental Stewardship: Students can apply this knowledge to evaluate local farming practices. For example, they can critically assess the use of agrochemicals in their communities, advocate for safer alternatives, or suggest better methods for waste disposal to prevent pollution. Understanding the effects of bush burning or deforestation equips them to become advocates for environmental protection and responsible land management.