Use of Biological Resources

Food Production and Agriculture – Revision Notes

Key Definitions and Terminology

• **Selective breeding (artificial selection):** The process by which humans choose organisms with desirable characteristics and breed them together to produce offspring with those desired traits.
• **Fertiliser:** A substance added to soil to provide mineral ions (e.g., nitrates, phosphates, potassium) that improve plant growth and increase crop yield.
• **Pesticide:** A chemical substance used to kill organisms (pests) that damage crops or reduce yield, including insecticides, herbicides, and fungicides.
• **Biological control:** The use of a natural predator, parasite, or pathogen to reduce the population of a pest organism, as an alternative to chemical pesticides.
• **Fish farming (aquaculture):** The controlled rearing of fish in enclosed spaces (ponds, cages, tanks) to produce food efficiently on a commercial scale.
• **Monoculture:** The agricultural practice of growing a single crop species over a large area, which can increase efficiency but may reduce biodiversity and increase susceptibility to disease.

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Main Concepts

1. Selective Breeding in Agriculture

• Humans have selectively bred plants and animals for thousands of years to enhance desirable characteristics.
• The process involves:

1. **Selecting** individuals with the desired characteristic from the population.
2. **Breeding** these selected individuals together.
3. **Selecting** the best offspring from the next generation.
4. **Repeating** this process over many generations until the desired trait is consistently expressed.

• In **plants**, desired characteristics include: higher crop yield, disease resistance, larger fruit, better taste, drought tolerance.
• In **animals**, desired characteristics include: higher milk yield in cattle, increased egg production in hens, faster growth rate, leaner meat.
• **Limitation:** Selective breeding reduces genetic variation (the gene pool narrows), which can make populations more vulnerable to disease or environmental change. This is known as **inbreeding depression**.

2. Increasing Crop Yields Using Fertilisers

• Plants require mineral ions for healthy growth:
• **Nitrates** – for amino acid and protein synthesis (growth of stems and leaves)
• **Phosphates** – for DNA, RNA, and ATP production (root growth and energy transfer)
• **Potassium** – for enzyme function and photosynthesis
• Fertilisers replace mineral ions removed from the soil when crops are harvested.
• **Types of fertiliser:**
• *Natural/organic fertilisers* – manure, compost (release minerals slowly)
• *Artificial/inorganic fertilisers* – manufactured chemicals (release minerals quickly, precise formulation)
• **Problem:** Excess fertiliser can be washed into waterways by rain (**leaching**), leading to **eutrophication** – this causes algal blooms, blocks light, kills aquatic plants, bacteria decompose dead matter and use up oxygen, leading to death of aquatic organisms.

3. Pest Control Methods

• Pests reduce crop yield by eating crops, competing for resources, or spreading disease.
• **Chemical control (pesticides):**
• Fast-acting and effective over large areas
• Disadvantages: may kill beneficial organisms (e.g., bees, natural predators), pests may develop resistance, chemicals may accumulate in food chains (**bioaccumulation**), may persist in the environment
• **Biological control:**
• Uses living organisms to control pest populations
• Advantages: no chemical pollution, target-specific, self-sustaining
• Disadvantages: the introduced control organism may become a pest itself, may not completely eliminate the pest, slow to take effect, difficult to control once released

4. Fish Farming (Aquaculture)

• Fish farming aims to produce large quantities of fish efficiently and economically.
• Methods used to maximise production:
• **Controlling water quality** – monitoring oxygen levels, pH, and temperature
• **Controlling feeding** – providing high-protein food in regulated amounts to maximise growth rate
• **Preventing disease** – using antibiotics or antifungal treatments; removing sick fish
• **Restricting movement** – keeping fish in enclosures/nets so they use less energy for movement, meaning more energy is converted into body mass (growth)
• **Selective breeding** – breeding fish that grow quickly or are disease-resistant
• **Removing predators** – using nets/barriers to prevent predation
• **Concerns:** pollution of surrounding water with waste/chemicals, escaped farmed fish interbreeding with wild populations (reducing genetic diversity), spread of disease to wild fish, ethical considerations about animal welfare.

5. Balancing Food Production with Environmental Impact

• Intensive farming methods increase food production to meet the demands of a growing global population.
• However, these methods can reduce biodiversity, pollute water and soil, and damage ecosystems.
• Sustainable approaches aim to balance high yield with minimal environmental harm, such as **integrated pest management** (combining biological control with minimal pesticide use), **crop rotation**, and responsible use of fertilisers.

6. Glasshouses and Polythene Tunnels

• Plants can be grown in **glasshouses** (greenhouses) where environmental conditions are controlled:
• **Temperature** is kept at optimum levels for enzyme activity and photosynthesis
• **Carbon dioxide concentration** can be increased (e.g., using paraffin heaters) to increase the rate of photosynthesis
• **Light intensity** can be supplemented with artificial lighting
• **Watering** is controlled to prevent water stress
• Pests and diseases are easier to manage in enclosed environments
• This allows crops to be grown **out of season** and in regions where they would not normally grow, increasing overall food production.

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Worked Examples and Real-World Applications

Example 1: Selective Breeding of Cattle for Milk Yield

A farmer wants to increase the average milk yield of their dairy herd.

• **Step 1:** The farmer identifies the cows with the highest milk production and the bulls whose mothers had high milk yields.
• **Step 2:** These individuals are bred together (or artificial insemination is used with semen from high-yield bulls).
• **Step 3:** From the offspring, the females with the highest milk yield are selected.
• **Step 4:** These are bred with bulls from other high-yielding lines.
• **Step 5:** This process is repeated over many generations.
• **Result:** Over time, the average milk yield of the herd increases significantly. Modern dairy cows can produce over 20,000 litres of milk per year, compared with around 1,000 litres from unselected breeds.
• **Trade-off:** The herd has reduced genetic variation, making it more susceptible to new diseases.

Example 2: Biological Control – Cactoblastis Moth in Australia

• **Problem:** Prickly pear cactus (*Opuntia*) was introduced to Australia and spread uncontrollably, covering millions of hectares of farmland and making it unusable.
• **Solution:** The *Cactoblastis cactorum* moth was introduced from South America. Its larvae feed on and destroy prickly pear cactus.
• **Outcome:** The cactus population was dramatically reduced, and farmland was restored.
• **Key point:** This is a successful example, but biological control does not always work — the introduced organism may not thrive, or it may itself become invasive (e.g., cane toads in Australia were introduced to control beetles but became a major pest themselves).

Example 3: Fish Farming of Salmon

• Salmon are reared in large net cages in sea lochs (Scotland) or fjords (Norway).
• Young salmon (fry) are hatched in freshwater hatcheries, then transferred to sea cages.
• They are fed high-protein pellets and monitored for disease.
• Movement is restricted by the cage, reducing energy loss through locomotion.
• Antibiotics may be added to food to prevent bacterial infections.
• **Environmental concerns:** Waste from cages pollutes surrounding water; sea lice from farmed salmon can infect wild salmon populations; escaped fish may interbreed with wild populations, reducing their genetic fitness.

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Exam Technique Tips

Tip 1: Use Comparative Language in Selective Breeding Questions

Edexcel mark schemes award marks for clear comparisons and sequences. When describing selective breeding, always structure your answer as a step-by-step process: *select → breed → select from offspring → repeat over many generations*. Do not just say "breed the best ones" — you must state that it is done over many generations and that you select from the offspring each time. Examiners look for the idea of repetition across generations, and omitting this commonly costs a mark.

Tip 2: Distinguish Clearly Between Advantages and Disadvantages

In questions comparing chemical pest control and biological control, Edexcel mark schemes require specific and developed points — not vague statements. For example:

• ❌ "Biological control is better for the environment" (too vague — no mark)
• ✅ "Biological control does not pollute the environment with chemicals that may accumulate in food chains" (specific — mark awarded)

Always link your point to a consequence or mechanism. Similarly, when discussing disadvantages of biological control, state that the introduced organism "may not be controllable once released" or "may itself become a pest and harm native species." The mark scheme rewards precision and developed reasoning.

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*End of revision notes for Food Production and Agriculture.*