Ecosystems And Tropic Levels - Part 2 (T4)

Question 1

Describe a food chain where the Polar bear is the “top carnivore”

Answer 1

Plankton > crustacean > fish > rigged seal > polar bear

Question 2

In a food chain, what is the name of the fourth consumer?

Answer 2

The quaternary consumer

Question 3

Describe a typical woodland food chain…

Answer 3

Green plant > cricket > wood mouse > snake > eagle

Question 4

Food chains can sometimes over simplify the situation so we can draw a “food web”. What does this kind of diagram show that food chains do not?

Answer 4

• they give some indication of the interrelationships that exists between various food chains in an ecosystem
• they can allow you to predict how changes in the numbers of an organism in one food chain may affect those in another food chain

Question 5

Like food chains, food webs also have their limitations. What are they and what would we use to present info about feeding relationships in an ecosystem instead?

Answer 5

• they do not give us any information about the quantity or mass of the organisms involved
• they do not show the role of the decomposers
• to see the above, we can use “ecological pyramids” or “energy flow diagrams”

Question 6

What is an ecological pyramid and what are the two main types?

Answer 6

• an ecological pyramid is a diagram that represents the relative amount of organisms at each trophic level in a food chain. The two main types are:
• pyramids of numbers, which represent the number of organisms in each trophic level in a food chain
• pyramids of biomass, which illustrate the total mass of the organisms in each trophic level

Question 7

Giving an example, explain why the feeding relationships in ecosystems result in a pyramid shape when presented as ecological pyramids (mainly pyramids of biomass)

Answer 7

• when a rabbit eats grass, not all the material in the grass will end up as rabbit
• some of the grass is not eaten
• some is not digested / absorbed
• some of the material are absorbed from excretory products
• many of the materials undergo restorations to release energy, and lose carbon dioxide and water
• only a small amount of the material from the grass actually ends up in the new cells of the rabbit
• losses are repeated at each stage in the food chain, so that smaller and smaller amounts of biomass are available for growth at successive trophic levels

Question 8

What are energy flow diagrams with regards to ecosystems and what are the main ideas behind them?

Answer 8

The concept of energy diagrams focuses on the energy transfer between trophic levels in the whole ecosystem

The key ideas behind them are:

• the process of photosynthesis ‘fixes’ sunlight energy into chemicals (eg, glucose and starch)
• respiration releases energy from compounds (eg, glucose)
• energy from respiration is used by almost all other biological processes (eg, muscle contractions, growth, reproduction, excretion and active transport)
• if energy released from respiration is used to produce. Ew cells (eg, body cells in growth and gametes or sex cells in reproduction) then th energy remains ‘fixed’ in molecules in that organism. However, through feeding the energy can be passed onto the next trophic level
• if respiratory energy is used for other processes then once it has been used it will escape to the surroundings as heat from the organism

Thus, energy is lost from food chains and webs at each trophic level

The energy lost can be shown in an energy flow diagram

Question 9

Approx what % of energy entering a trophic level is passed onto the next trophic level, and what does this explain?

Answer 9

• around 10%
• this explains why many food chains do not have more than five trophic levels

Eg: A > B > C > D > E

10% of 100% enters B from A, then 1% enters C, then 0.1% into D etc…

Question 10

Why are microorganisms important in terms of ‘recycling’?

Answer 10

The break down complex organic molecules in the bodies of dead animals and plants into simpler substances, which are then released into the environment

Question 11

How is the soil able to constantly provide plants with the minerals they need to grow?

Answer 11

When plants and animals decay, the same minerals are absorbed back into the soil and used over and over again, or recycled

Question 12

Over the past 200 years the carbon levels in the atmosphere haven’t changed much. Why?

Answer 12

Because carbon, like minerals, is constantly recycled

Question 13

Describe four processes which are important in the cycling of carbon through ecosystems…

Answer 13

• photosynthesis: enables carbon atoms from as carbon dioxide to be part of organic compounds in plants
• feeding and assimilation: passes carbon atoms already present in organic compounds along food chains (ie: in material eaten by animals and then assimilated within the animal’s body cells)
• respiration: produces carbon dioxide from the breakdown of organic compounds (mainly carbohydrates) as they are broken down to release energy. The carbon dioxide is returned to the atmosphere
• fossilisation: this occurs when some living things do not fully decay when they die. Eg, if the soil is acidic, fossil fuels are formed. Combustion of fossil fuels then releases carbon dioxide into the atmosphere