unit 3

• What is the overall (summary) word equation for photosynthesis?

  carbon dioxide + water -> sugar + oxygen
• What is the name of the pigment that traps light energy and in what part of a plant cell is it found?

  chlorophyll, in the chloroplast
• Describe what happens during the stage 1 of photosynthesis (the light reactions).

  Light energy is converted into chemical energy (ATP):

  1) Water is split to produce hydrogen and oxygen.

  2) The energy released is used to generate ATP

  3) Oxygen diffuses from the cell.
• Which two products of the light reactions are required for stage 2 of photosynthesis (carbon fixation)?

  ATP and hydrogen
• What is carbon fixation (stage 2 of photosynthesis)?

  A series of enzyme-controlled reactions, which use hydrogen and ATP (produced by the light reactions) with carbon dioxide to produce sugar.
• What happens to the chemical energy in the sugar that is produced during photosynthesis?

  1) Some of it is used for respiration

  2) Some of it is turned into a structural carbohydrate (cellulose)

  3) Some of it is turned into a storage carbohydrate (starch)See an expert-written answer!We have an expert-written solution to this problem!
• Name an example of a limiting factor for photosynthesis and plant growth.

  1) carbon dioxide concentration

  2) light intensity

  3) temperature
• How can a farmer increase the photosynthetic rate and therefore growth of her crops?

  She could increase the carbon dioxide concentration in a greenhouse, or increase light intensity by adding artificial lighting, or increase temperature by adding heaters.
• Why has there been a demand for higher food yield in recent years?

  There has been an increase in the human population.
• Why do farmers use fertilisers?

  Fertilisers provide chemicals such as nitrates. By increasing nitrate content of the soil they can increase crop yield.
• Why do farmers use pesticides?

  Plants and animals that reduce plant yield can be killed by pesticides.
• What happens to the nitrates that are dissolved in soil water?

  1 - absorbed by plants.

  2 - plants use nitrates to make amino acids

  3 - plants use amino acids to make plant proteins
• How do animals get amino acids for making animal proteins?

  They eat plants or other animals to get amino acids.
• What is the cause of algal blooms?

  Fertilisers leach into fresh water, adding extra unwanted nitrates. This will increase algal populations which can cause algal blooms.
• Why do algal blooms kill aquatic plants?

  They reduce light levels.
• Why do algal blooms cause an increase in the number of bacteria in fresh water?

  Algal blooms kill aquatic plants. The dead aquatic plants and the algae become food for decomposing bacteria, which allows them to increase in number.
• Following an algal bloom there is an increased number of decomposing bacteria in the water. Name a negative consequence of having more bacteria in the water.

  The bacteria use up oxygen when they respire, reducing oxygen availability for other organisms.
• What are some problems associated with using pesticides (such as DDT) on crops?

  - pesticides can accumulate in the bodies of organisms over time

  - they are passed along the food chain

  - the toxicity increases to lethal levels
• What are two ways of increasing plant yield without using pesticides?

  - biological control

  - Create GM (genetically modified) crops that resist pests.
• What is an alternative to using fertilisers?

  We can use genetically modified (GM) crops that are better able to grow in low nitrate soils.
• What is biological control?

  The use of a predator or parasite to control a pest species.
• Give an example of biological control

  - Controlling aphids by releasing ladybirds (their predators)
• What is a mutation?


  A random change to genetic material.
• What are the three types of mutation that can arise?

  - neutral

  - advantageous to survival

  - disadvantageous to survival
• Why are mutations important in evolution?

  They are the only source of new alleles.
• Name a factor that can increase the rate of mutation.

  - radiation (e.g. X-rays and UV light)

  - some chemicals (e.g. mustard gas).
• What is an adaptation?


  An inherited characteristic that makes an organism well suited to survival in its

  environment/niche.
• Describe the process of natural selection in four main points.

  - species produce more offspring than the

  environment can sustain.

  - Survival of the fittest occurs when there are

  selection pressures.

  - The best adapted individuals in a population survive to reproduce passing on their favourable alleles

  - these alleles increase in frequency within the population
• What is speciation?


  The formation of two different species from one.
• Give an example of an isolation barrier in speciation.

  - geographical

  - ecological

  - behavioural
• Why are isolation barriers important in speciation?

  They stop the populations Interbreeding.
• Describe the process of speciation in four main points.

  - two populations of a species become isolated by a barrier

  - different mutations occur in each sub-population.

  - natural selection selects for different mutations in each group due to different selection pressures.

  - each population evolves until they become so genetically different they are two different

  species.
• Energy is transferred from one level of the food chain to the next. How much of this energy is used for growth?

  Very little.
• The majority of energy is lost when it is transferred to one level of the food chain to another. How is it lost?

  - heat

  - movement

  - undigested material
• Some food chains make irregular pyramids of numbers, as the producer may be a large organism (e.g. oak tree). How would you represent this food chain as a true pyramid?

  By creating a pyramid of energy.See an expert-written answer!We have an expert-written solution to this problem!
• Which type of organism is found at the base of a pyramid of numbers or pyramid of energy?

  The producer
• Which type of organism is found at the apex (tip) of a pyramid of numbers or pyramid of energy?

  The top level consumer
• Give an example of a biotic factor that could affect biodiversity.

  - competition for resources

  - disease

  - food availability

  - grazing

  - predation
• Give an example of an abiotic factor that could affect biodiversity.

  - light intensity

  - moisture

  - pH

  - temperature
• What is an ecosystem?

  All the organisms (the community) living in a particular habitat and the non-living components with which they interact.