Edexcel International GCSE Biology 4BI1: Use of biological resources – Study Guide

This study guide teaches Topic 5, Use of biological resources (specification points 5.1–5.20), of the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3. The qualification is untiered. Points with a B reference (5.9B and 5.17B–5.20B) are bold in the specification and are examined on Paper 2 only; everything else can appear on either paper. It applies to the June and November series examined under Issue 3.

Use it with the revision notes and the practice questions. The full course is on the Edexcel IGCSE Biology hub, and the printable checklist lists every point.

What this topic covers

Spec point	What you must be able to do	Paper
5.1–5.2	Glasshouses and polythene tunnels; effect of more CO₂ and higher temperature on yield	1 and 2
5.3–5.4	Fertiliser; pest control with pesticides and biological control	1 and 2
5.5–5.7	Yeast in bread; practical on anaerobic respiration in yeast; Lactobacillus in yoghurt	1 and 2
5.8	Industrial fermenters and the conditions they provide	1 and 2
5.9B	Fish farming	Paper 2 only
5.10–5.11	Selective breeding of plants and animals	1 and 2
5.12–5.16	Restriction enzymes, ligase, vectors, GM insulin, GM crops, “transgenic”	1 and 2
5.17B–5.20B	Micropropagation, cloning mammals (Dolly), cloned transgenic animals	Paper 2 only

(a) Food production: crop plants

Glasshouses and polythene tunnels (5.1)

Both let light in and trap heat, so the air inside is warmer than outside. They also:

• protect crops from frost, wind, heavy rain and some pests
• extend the growing season, so crops can be grown earlier or out of season
• let the grower control conditions: temperature, carbon dioxide, water supply and sometimes artificial lighting.

Polythene tunnels are cheaper and easier to put up over field crops but give less control than a glasshouse.

Carbon dioxide and temperature (5.2)

Photosynthesis is limited by whichever factor is in shortest supply. Outside, carbon dioxide concentration and temperature often limit the rate. In a glasshouse, growers burn paraffin or gas, which releases carbon dioxide and heat.

• More carbon dioxide → faster photosynthesis → more glucose for growth → higher yield.
• Higher temperature → enzymes controlling photosynthesis work faster → higher yield, up to the optimum.

Both effects level off once another factor (often light) becomes limiting. Too high a temperature denatures enzymes and reduces growth. So a grower raises carbon dioxide and temperature only while the extra yield is worth more than the fuel.

Worked example 1. A tomato grower raises carbon dioxide in a glasshouse. The yield rises from 32 kg per m² to 40 kg per m². Calculate the percentage increase.

Percentage change = (new − original) ÷ original × 100
                  = (40 − 32) ÷ 32 × 100
                  = 8 ÷ 32 × 100 = 25%

Fertiliser (5.3)

Plants need mineral ions from the soil. Intensive cropping removes them. Fertiliser (manure or artificial) replaces them.

• Nitrate ions are used to make amino acids and proteins for growth.
• Magnesium ions are used to make chlorophyll.

More protein and chlorophyll → more growth and photosynthesis → higher yield. Too much fertiliser can be leached into rivers and cause eutrophication (see Topic 4, Ecology and the environment).

Pest control (5.4)

Pests (insects, fungi, weeds) reduce yield. They eat crops, spread disease, or compete with crops for light, water and minerals.

	Pesticides	Biological control
Method	Chemicals that kill pests	A predator, parasite or pathogen of the pest is introduced
Advantages	Act quickly; easy to apply; kill most of the pest	Specific to the pest; no chemical residues on food; self-sustaining once established; pests do not become resistant
Disadvantages	Kill non-target species, including useful insects; can build up along food chains; pests can become resistant; must be reapplied; residues on food	Slow; does not wipe out the pest; the control organism may eat other species or itself become a pest

(a) Food production: micro-organisms

Yeast and bread (5.5)

Yeast is a single-celled fungus. In bread-making, yeast is mixed with flour, sugar and warm water.

1. Enzymes break starch in the flour into sugars.
2. Yeast respires, first aerobically then anaerobically, producing carbon dioxide and ethanol.
3. Carbon dioxide bubbles are trapped in the dough, so it rises.
4. Baking kills the yeast, evaporates the ethanol and sets the bread.

Word equation: glucose → ethanol + carbon dioxide (anaerobic respiration in yeast).

Practical: anaerobic respiration in yeast (5.6)

Mix yeast with sugar solution in a boiling tube. Cover the surface with a layer of oil to keep oxygen out. Connect a delivery tube to a gas syringe or into water, and measure the volume of gas, or count bubbles, in a fixed time. Change one condition, such as temperature or sugar concentration. Keep the others the same: mass of yeast, volume and concentration of sugar solution, time to equilibrate in the water bath.

Worked example 2. At 25 °C, 9.0 cm³ of gas is collected in 6 minutes. At 35 °C, 18.0 cm³ is collected in 6 minutes.

Rate at 25 °C = 9.0 ÷ 6 = 1.5 cm³ per minute
Rate at 35 °C = 18.0 ÷ 6 = 3.0 cm³ per minute

The rate doubles, because the enzymes for respiration work faster at 35 °C. At much higher temperatures they denature and the rate falls.

Lactobacillus and yoghurt (5.7)

1. Milk is heated (pasteurised) to kill other bacteria, then cooled.
2. Lactobacillus bacteria are added.
3. The mixture is kept warm (incubated) for several hours.
4. The bacteria ferment lactose into lactic acid.
5. The acid lowers the pH, so milk proteins clot and thicken. The acid gives yoghurt its sour taste and slows the growth of other microorganisms.

Industrial fermenters (5.8)

A fermenter is a large steel vessel for growing microorganisms in huge numbers.

Condition	How it is provided	Why
Aseptic precautions	Vessel sterilised with steam; air filtered; nutrients sterilised	Contaminating microbes would compete for nutrients or make unwanted or toxic products
Nutrients	Sugar (energy source) and a nitrogen source such as amino acids or ammonium salts	For respiration and making proteins for growth
Optimum temperature	Water jacket; probe; cooling water removes heat released by respiration	Enzymes work fastest; overheating would denature them
Optimum pH	pH probe; acid or alkali added	Enzymes work best at their optimum pH
Oxygenation	Sterile air pumped in	For aerobic respiration
Agitation	Motor-driven paddles stir the mixture	Keeps microbes, nutrients, oxygen and heat evenly spread

Fish farming (5.9B) – Paper 2 only

Fish farms produce large amounts of protein in a small area. Farmers control:

• Water quality: oxygen level kept high; water filtered or changed.
• Intraspecific predation (fish eating their own species): fish kept in tanks by size or age.
• Interspecific predation (other species eating the fish): nets over tanks; only one species per tank.
• Disease: fish kept at a controlled density; antibiotics or pesticides for parasites used; sick fish removed.
• Waste products: removed by filtering or water flow, so they do not pollute the water.
• Feeding: high-protein food given little and often, so there is no uneaten waste and growth is fast.
• Selective breeding: fish chosen for fast growth or disease resistance.

(b) Selective breeding (5.10, 5.11)

1. Choose parents that show the desired characteristic.
2. Breed them together.
3. Select the offspring that show the characteristic most strongly.
4. Breed these together.
5. Repeat over many generations.

Plants: high yield, disease resistance, short stems (less wind damage), drought tolerance. Animals: cattle with high milk yield or more meat, sheep with more wool, hens that lay more eggs.

Selective breeding is slow and reduces variation in the population, so it may be harder for the population to survive a new disease.

(c) Genetic modification (5.12–5.16)

• Restriction enzymes cut DNA at specific base sequences, often leaving short single-stranded “sticky ends”.
• Ligase enzymes join pieces of DNA together.
• Vectors carry DNA into another cell. Plasmids are small circles of DNA in bacteria. Viruses can be used because they insert their DNA into the host cell.
• DNA made by combining DNA from two sources is recombinant DNA.
• Transgenic means genetic material has been transferred from one species to a different species.

Human insulin from bacteria (5.14)

1. The human insulin gene is cut out with a restriction enzyme.
2. A plasmid is cut with the same restriction enzyme, so the sticky ends match.
3. The gene and plasmid are joined with ligase, forming a recombinant plasmid.
4. The plasmid is put into a bacterium.
5. The bacteria are grown in a fermenter. They multiply and each one makes human insulin.
6. Insulin is extracted and purified.

GM plants (5.15)

Genes can give crop plants resistance to insect pests (less damage, fewer pesticides), resistance to herbicides (weeds can be sprayed without harming the crop), tolerance of drought, or higher nutritional value. Each can raise the yield or quality of food.

(d) Cloning (5.17B–5.20B) – Paper 2 only

Micropropagation (5.17B, 5.18B)

1. Small pieces of tissue (explants) are cut from the tips of a parent plant.
2. The surfaces are sterilised.
3. Explants are placed on sterile agar containing nutrients and plant hormones, in vitro.
4. They grow into small plantlets, which are moved to compost.

Thousands of plants can be produced quickly from one parent, in a small space, at any time of year. They are genetically identical, so all show the parent’s desirable characteristics, such as flower colour or high yield. The drawback is no variation: one disease could affect every plant.

Cloning a mammal: Dolly the sheep (5.19B)

1. A diploid body cell (from the udder) is taken from sheep A.
2. An egg cell is taken from sheep B, and its nucleus is removed (enucleated).
3. The diploid nucleus from sheep A is inserted into the enucleated egg; an electric shock makes it divide.
4. The embryo develops and is placed in the uterus of a surrogate sheep C.
5. The lamb is genetically identical to sheep A.

Cloned transgenic animals (5.20B)

A human gene for a useful protein is inserted into an animal embryo, so the animal produces the protein, for example in its milk. That transgenic animal can then be cloned, giving a herd that all make the human protein, which is extracted from the milk.

Common errors

• Saying yeast makes bread rise by producing ethanol. It is carbon dioxide.
• Writing that restriction enzymes “join” DNA. They cut; ligase joins.
• Forgetting the plasmid must be cut with the same restriction enzyme.
• In Dolly, saying the clone is identical to the egg donor or surrogate. It matches the nucleus donor.
• Giving only advantages of biological control when asked to compare.

Next steps

Condense this with the revision notes, then test yourself with the practice questions. The free diagnostics show which Biology topics need the most work.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1) specification, Issue 3, first examination June 2019, Pearson Education Limited – Topic 5, Use of biological resources.