Food Production (Edexcel IGCSE Science (Double Award): Biology): Flashcards

True.

They prevent the entry of pests that damage plants and diseases that can kill them.

False.

Too high a temperature denatures the enzymes controlling photosynthesis, so tropical glasshouses need ventilating.

• Temperature

• Light intensity

• Carbon dioxide concentration

The factor in shortest supply at a given time, which restricts the rate of a process such as photosynthesis.

Because the reaction is controlled by enzymes, which work faster as temperature rises.

Beyond a certain temperature the enzymes begin to denature, so the rate of reaction decreases.

Carbon dioxide is a raw material for photosynthesis, so the more present, the faster the reaction — until another factor becomes limiting.

The more light a plant receives, the faster the rate — until another required factor is in short supply.

Only the plant's own ability to absorb these materials and make them react.

Raising the temperature increases photosynthesis because the reaction is controlled by enzymes.

Above the optimum temperature the enzymes controlling photosynthesis begin to denature.

False.

Only until another factor, such as light or temperature, becomes the limiting factor.

True.

That is why increasing its concentration in a glasshouse can raise crop yields.

Because plants rarely have unlimited supplies of light, carbon dioxide, water and warmth, so whichever is lowest restricts the rate.

They increase the key nutrients in the soil, so crop plants grow larger and healthier, and faster and bigger — raising yields.

Because crop plants take mineral ions up from the soil, so they must be replaced if crops are grown in the same field year after year.

• Farmyard manure

• Compost

As dry granules spread on the soil, or sprayed on in liquid form.

Needed for making chlorophyll.

A deficiency causes yellowing of the leaves.

Needed for making amino acids, the building blocks of proteins.

A deficiency causes weak growth and yellowing of the leaves.

• Magnesium ions — for making chlorophyll

• Nitrate ions — for making amino acids

The excess is leached into rivers and lakes, where it causes eutrophication — so more fertiliser does not always mean a better outcome.

Magnesium ions are needed by a plant to make chlorophyll.

Farmyard manure and compost are examples of organic fertilisers.

True.

Both cause yellowing of the leaves, though nitrate deficiency also causes weak growth.

False.

Plants take up nitrate ions from the soil — not nitrogen gas.

A chemical that kills unwanted species, reducing damage to crops and increasing yields.

• Insects and other animals damage crops by eating them

• Weeds compete with crops for space, water and nutrients

• Fungi infect crops and spread diseases

• Insecticides — kill insect pests

• Herbicides — kill weed species

• Fungicides — kill fungal pests

• Easily accessible and relatively cheap

• Have an immediate effect

• Can kill the entire population of pests

• Pests can develop resistance to them

• They are non-specific and can kill beneficial organisms, such as pollinating bees

• They can be persistent and bioaccumulate in top predators

• They must be repeatedly applied

When a persistent chemical does not break down in the body and builds up in great concentrations at the top of food chains, harming top predators.

Using a natural predator to eat a pest species, reducing the pest's impact on crop yields.

• Ladybirds eating aphids, which happens naturally

• Parasitic wasps introduced to control whitefly in glasshouse tomato crops

Because it is based on a predator-prey cycle, so it keeps the pest at lower levels rather than eliminating it.

• A natural method, so no pollution

• No resistance develops

• Can target specific species

• Long lasting, and does not need repeated application

• May eat other organisms instead of the pest

• Takes longer to be effective

• Cannot kill the entire population

• May not adapt, may move away, or may become a pest itself

Chemicals that kill weed species are called herbicides.

Persistent pesticides can build up in top predators, a process called bioaccumulation.

False.

No resistance develops with biological control — that is one of its advantages over pesticides.

True.

Pesticides are non-specific, so they can kill beneficial organisms such as the bees that pollinate crops.

A single-celled fungus that can carry out both aerobic and anaerobic respiration.

It produces enzymes that break down the starch in flour, releasing sugars it can use in respiration.

It respires aerobically at first, then switches to anaerobic respiration when the oxygen runs out.

Alcohol (ethanol) and carbon dioxide.

The carbon dioxide produced by the yeast is trapped in small air pockets in the dough, increasing its volume.

Any ethanol produced by the yeast is evaporated by the heat during baking.

It is killed by the high temperatures, so there is no further respiration.

glucose → ethanol + carbon dioxide

Bread dough rises because carbon dioxide produced by the yeast is trapped in the dough.

Yeast is a single-celled fungus that can respire with or without oxygen.

False.

Yeast can carry out both aerobic and anaerobic respiration, switching to anaerobic when oxygen runs out.

False.

The high temperatures kill the yeast, which stops any further respiration.

Ethanol and carbon dioxide. The process is called fermentation.

Mix yeast with sugar solution in a boiling tube, to provide glucose.

Add a layer of oil on top.

Connect the tube by a delivery tube to another boiling tube of limewater.

Place in a water bath at a set temperature and count the bubbles produced in a fixed time, such as 2 minutes.

Repeat at different temperatures.

To prevent oxygen entering the solution, so the yeast cannot respire aerobically.

By the rate at which carbon dioxide is produced — counting the bubbles given off in a fixed time.

It shows that the gas being produced is carbon dioxide, by turning cloudy.

The temperature moves closer to the optimum for the yeast's enzymes, increasing enzyme activity and so the rate of respiration.

The enzymes denature, so carbon dioxide production slows down and eventually stops.

• The concentration, volume and pH of the sugar solution

• The mass of yeast added

• The species of yeast used

It is used in the manufacture of bread, where carbon dioxide makes the dough rise, and of alcoholic drinks, since ethanol is a type of alcohol.

Anaerobic respiration in yeast cells is called fermentation.

A layer of oil on the yeast solution stops oxygen getting in.

True.

That is why the rate rises with temperature towards the optimum and then falls as the enzymes denature.

False.

Only up to the optimum temperature. Above it, the enzymes denature and the rate falls.

Lactobacillus.

• They can produce complex molecules, such as the enzymes that turn milk into yoghurt

• They reproduce rapidly, so the amount of chemical they produce increases quickly

Sterilise all equipment.

Pasteurise the milk at 85–95 °C.

Cool it to 40–45 °C and add Lactobacillus.

Incubate for several hours while the bacteria digest milk proteins and ferment the lactose.

Cool to 5 °C, then stir and add any flavourings before packaging.

To kill other, unwanted bacteria, which could otherwise compete for the lactose and spoil the taste of the yoghurt.

It converts the lactose into lactic acid.

The increased acidity sours and thickens the milk, forming yoghurt.

It prevents the growth of other, possibly harmful microorganisms, so the yoghurt keeps longer than fresh milk.

To halt the action of the *Lactobacillus* bacteria.

40–45 °C — warm enough for the bacteria to work quickly, but not hot enough to kill them.

Lactobacillus converts the lactose in milk into lactic acid.

Before the bacteria are added, the milk is pasteurised at 85–95 °C to kill unwanted bacteria.

True.

The lowered pH prevents the growth of other microorganisms, acting as a preservative.

False.

They would slow it down by competing with the *Lactobacillus* for the lactose, and could spoil the taste.

A container used to grow (culture) microorganisms such as bacteria and fungi in large amounts.

• Making yoghurt

• Making mycoprotein

• Producing genetically modified bacteria

• Growing moulds that produce antibiotics, such as penicillin

Conditions can be carefully controlled, producing large quantities of exactly the right type of microorganism.

The fermenter is cleaned by steam to kill microorganisms and prevent chemical contamination, so that only the desired microorganism grows.

They are used in respiration to release energy for growth, and ensure the microorganisms can reproduce.

It is monitored with probes and maintained using a water jacket.

This keeps enzymes at their optimum — too hot and they denature, too cold and they work too slowly.

It is monitored with a probe and adjusted if necessary using acids or alkalis, to keep it at the optimum for that microorganism.

So that aerobic respiration can take place.

Stirring paddles ensure microorganisms, nutrients, oxygen, temperature and pH are evenly distributed throughout the fermenter.

Temperature in a fermenter is maintained using a water jacket around the vessel.

A fermenter is cleaned with steam to kill unwanted microorganisms.

True.

Agitation evenly distributes microorganisms, nutrients, oxygen, temperature and pH.

False.

They are also used for non-food processes, such as producing genetically modified bacteria and antibiotic-producing moulds.