Food production

Food Production: Using Biological Resources

In this chapter, we explore how biological resources are managed and manipulated to maximise food production for the human population. This covers crop farming, the use of microorganisms in food production and fermenters, and commercial fish farming.

1. Maximising Crop Yields

To increase crop yields, farmers optimise environmental factors for photosynthesis and protect crops from pests and nutrient deficiencies.

1.1 Glasshouses and Polythene Tunnels

Enclosed growing systems such as glasshouses (greenhouses) and polythene tunnels allow farmers to control the internal environment:

• Carbon Dioxide Concentration: Paraffin heaters or gas burners release \(\text{CO}_2\). Increasing carbon dioxide concentration prevents it from being a limiting factor for photosynthesis, increasing the rate of glucose production.
• Temperature: Trapped heat and artificial heaters maintain the optimum temperature for photosynthetic enzyme activity, preventing low temperatures from limiting the reaction rate while avoiding denaturation from excessive heat.
• Light: Transparent glass or polythene allows sunlight to enter, and supplementary artificial lighting can be used at night or during overcast weather to extend photosynthesis time.
• Water supply: Automated watering or irrigation systems supply consistent moisture.
• Protection: Enclosed structures protect crops from physical damage by wind and rain, as well as from insect pests.

1.2 Use of Fertilisers

Harvesting crops removes essential mineral ions from the soil. Fertilisers replace these nutrients:

• Nitrates: Provide nitrogen needed to synthesise amino acids and proteins for growth.
• Magnesium: Essential for the synthesis of chlorophyll, which absorbs light for photosynthesis.
• Phosphates and Potassium: Support root development, energy transfer (ATP), and overall cellular metabolism.

Fertilisers can be organic (such as manure or compost, which release minerals slowly and improve soil structure) or inorganic (chemical salts that dissolve quickly and are rapidly absorbed by plant roots).

1.3 Pest Control

Pests (weeds, insects, fungi, and molluscs) reduce yield by eating crops, competing for light, water, and nutrients, or transmitting disease. Farmers control pests using two main strategies:

Chemical Pesticides

• Definition: Chemical substances (insecticides, herbicides, fungicides) sprayed to kill pests.
• Advantages: Fast-acting, readily available, and easy to apply over large areas.
• Disadvantages: Pests can develop genetic resistance over time; non-target beneficial species (such as pollinators) may be killed; chemicals can wash into water bodies and cause bioaccumulation along food chains.

Biological Control

• Definition: Introducing a natural predator, parasite, or pathogen to control a pest population (e.g. introducing ladybirds to feed on aphids).
• Advantages: Highly specific to the target pest; pests do not develop resistance; no toxic chemicals accumulate in the environment; provides long-term control.
• Disadvantages: Slower to reduce pest numbers; rarely completely eliminates the pest; introduced control agents can become invasive or attack unintended native species.

2. Microorganisms in Food Production

2.1 The Role of Yeast in Bread Making

Yeast (a single-celled fungus) respires both aerobically and anaerobically. In bread making, yeast is mixed with flour, water, and sugar to form dough.

When oxygen becomes depleted, yeast undergoes anaerobic respiration (fermentation):

\(\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}\)

• Bubbles of carbon dioxide gas become trapped within the gluten dough, causing the dough to rise and giving bread its light, spongy texture.
• During baking, high temperatures kill the yeast, stop fermentation, and cause the ethanol to evaporate.

Practical: Investigating Anaerobic Respiration in Yeast

A yeast and glucose suspension is placed in a boiling tube and covered with a layer of liquid paraffin (oil) on top to prevent oxygen from the air dissolving into the suspension, ensuring strictly anaerobic conditions. The rate of anaerobic respiration is measured by connecting a delivery tube to a gas syringe or counting the number of carbon dioxide bubbles produced per minute (or bubbling into limewater/indicator) at different controlled temperatures.

2.2 The Role of Bacteria in Yoghurt Production

Yoghurt production relies on the bacterium Lactobacillus (such as Lactobacillus bulgaricus):

1. Pasteurisation: Milk is heated to approximately \(85\text{--}90^{\circ}\text{C}\) to kill any pathogenic or competing bacteria, then cooled to \(40\text{--}45^{\circ}\text{C}\) so the bacteria added next are not killed or their enzymes denatured.
2. Inoculation: A starter culture of Lactobacillus is added.
3. Incubation: The mixture is maintained at \(40\text{--}45^{\circ}\text{C}\) (optimum temperature for bacterial enzymes) for several hours.
4. Fermentation: Lactobacillus feeds on the sugar lactose in milk, fermenting it into lactic acid.
5. Coagulation: The accumulation of lactic acid lowers the pH, causing milk proteins (casein) to denature and coagulate, turning the milk into a thick, semi-solid yoghurt with a sour taste that also acts as a natural preservative.

3. Industrial Fermenters

An industrial fermenter is a large, sterile vessel used to grow microorganisms (such as bacteria or fungi) at a commercial scale to produce substances like insulin, enzymes, or antibiotics.

4. Fish Farming (Paper 2 Only)

Fish farming (aquaculture) involves raising large quantities of fish in enclosed sea cages or freshwater tanks to maximise yield and prevent the overfishing of wild stocks.

Key management strategies include:

• Maintenance of Water Quality: Water in tanks is filtered and aerated to provide high levels of dissolved oxygen for aerobic respiration and to remove toxic metabolic wastes such as ammonia.
• Control of Interspecific Predation: Nets or physical barriers cover cages to stop different predatory species (e.g. birds, seals, larger predatory fish) from entering and eating the stock.
• Control of Intraspecific Predation: Fish of the same species are separated into different tanks or pens according to size and age to stop larger fish from attacking and eating smaller ones.
• Control of Disease: High stocking densities make fish prone to infectious diseases and parasites (such as sea lice). Water is kept clean, cages are regularly sterilised or rotated, and antibiotics or chemical treatments are administered when necessary.
• Quality and Frequency of Feeding: Fish are fed high-protein food to maximise growth. Feed is supplied frequently in small quantities to avoid uneaten food decaying at the bottom, which depletes dissolved oxygen and pollutes water.
• Selective Breeding: Individuals with desirable traits (e.g. rapid growth rate, high meat yield, calm temperament, and natural disease resistance) are chosen to breed across generations.

Chapter Summary Review

• Glasshouses and polythene tunnels boost crop yield by controlling \(\text{CO}_2\) levels, temperature, light, and water.
• Fertilisers replace essential soil minerals (nitrates for proteins, magnesium for chlorophyll).
• Pest control uses chemical pesticides (fast, but risks resistance and bioaccumulation) or biological control (specific natural enemies).
• Yeast respires anaerobically to produce \(\text{CO}_2\) (causes bread dough to rise) and ethanol.
• Lactobacillus ferments lactose into lactic acid, coagulating milk protein to produce yoghurt.
• Industrial fermenters maintain sterile conditions, optimum pH and temperature, nutrient supply, oxygenation, and agitation for maximum growth.
• Fish farming (P2) maximises yield through water quality maintenance, controlling predation (intraspecific and interspecific), disease management, controlled feeding, and selective breeding.