B4 - Plant Minerals and Decay

Question 1

How do the gardeners make sure the soil has enough minerals?

Answer 1

• adding manure, compost or rotting leaves which decays slowly and releases minerals
• adding chemical fertilisers, which dissolve and release minerals into the soil.

Question 2

What minerals do plants need and why? What are the deficiency symptoms?

Answer 2

1. Nitrogen contained in nitrates- make amino acids, which are used to build proteins for cell growth - Poor plant growth; yellow leaves
2. Phosphorus contained in phosphates- In respiration, to make ATP, also needed to make DNA and molecules in the cell membrane - Poor root growth; stunted plant; discoloured purple leaves
3. Potassium (K) - Needed by enzymes involved in photosynthesis and respiration. - Poor flower and fruit growth; yellowed leaves with brown spots
4. Magnesium (Mg) - Needed to make chlorophyll for photosynthesis - Yellow leaves, especially the lower leaves

Question 3

What is active transport and how do minerals use it?

Answer 3

Minerals are usually present in very low concentrations in the soil, lower than their concentration in the plant’s cells so the minerals cannot move into the cells by diffusion. So active transport is used :
• Active transport pumps particles against a concentration gradient (from low to high concentration).
• It requires energy from respiration in the molecule ATP.
• It needs a carrier protein in the membrane.

Question 4

What are the two main groups of microbes involved in decay?

Answer 4

Bacteria and fungi

Question 5

How do we use microbes to help us break down waste?

Answer 5

• Compost – gardeners use natural recycling processes. They gather their waste such as grass cuttings, leaves, and twigs. They pile these up or put them into a compost bin, and allow them to decay. The result is a nutrient-rich soil which can be used for growing plants.
• Sewage works – the sewerage produced in homes and factories is sent to a sewage works. Here bacteria digest the organic waste in large tanks, making the sewage clean enough to safely discharge into natural waterways.

Question 6

How do different conditions affect the rate of decay?

Answer 6

1. At warmer temperatures the rate of decay is faster - Microbes are able to respire faster, and will grow and reproduce quicker in warmer conditions.
2. The more oxygen, the faster the rate of decay - The more oxygen there is available, the faster the microbes will be able to respire. This will allow them to grow quicker and reproduce faster.
3. In moist conditions decay is faster - Microbes need water to remain healthy. In moist conditions the microbes will grow faster and reproduce more.

Question 7

What are the two main groups of decay organisms?

Answer 7

• Detritivores, such as earthworms, maggots, millipedes, and woodlice, eat small parts of the dead material, which they digest and then release as waste. This activity increases the surface area of the dead remains for decomposers to act on.
• Decomposers such as bacteria and fungi chemically break down dead material, releasing ammonium compounds into the soil.

Question 8

What is a saprophyte ?

Answer 8

Most decomposers are saprophytes. They feed by releasing enzymes onto the dead animal or plant. The enzymes digest the dead material in a process called extracellular digestion. The decomposers then absorb the digested chemicals.

Question 9

Describe some ways to prevent decay

Answer 9

• Canning - Food is sealed in a metal container. It is heated
  to kill any microbes. The can prevents the entry of oxygen and any decomposer microbes.
• Cooling - Food can be placed in a fridge, typically at 4 °C. At this temperature the reproduction of decomposers is slowed down.
  • Freezing - Freezers keep food at a lower temperature, often –5 °C. At this temperature decomposers stop reproducing.
  • Drying - Some foods are dried, such as pasta. Without water decomposers do not grow or reproduce.
• Adding salt - Some foods are salted, such as cured meats and fish. Salt causes water to be drawn out of the microbes by osmosis, and this kills them.
• Adding sugar - Other foods have sugars added, such as jams. The effect is the same as salting; water is withdrawn.
• Adding vinegar -Vinegar is an acid, which is added to foods such as pickled onions during pickling. The acid kills decomposers.

Question 10

What are some consequences of food decay?

Answer 10

• It reduces the amount of food for people to eat.
• In some areas of food shortage, decay of food stores could
cause malnutrition.
• Eating food that is decaying can lead to illness.
• The profits of farmers and supermarkets are reduced
when food decays before it is sold.