4.2.3 Food Pyramids & Transfer of Energy

Question 1

A pyramid of numbers shows, what?

Answer 1

how many organisms we are talking about at each level of a food chain.

Question 2

The width of the box indicates, what?

Answer 2

the number of organisms at that trophic level

For example, consider the following food chain:

Sun → Grass → Vole → Owl

Question 3

Describe how a pyramid of numbers for a food chain would look like?

Answer 3

An example would be;

Would first start with grass (as a large rectangle)

Then it would have a rodent (such a voles) as a medium rectangle

It would then have an Owl on a small rectangle

Question 4

Pyramids of numbers are not always, what?

Answer 4

pyramid-shaped

Question 5

(Rules to remember when drawing a pyramid of numbers) What can you not change?

Answer 5

You cannot change the trophic level of the organisms

– They must stay in the same order as in the food chain with producers on the bottom, followed by primary consumers, then secondary consumers, then tertiary consumers

Question 6

(Rules to remember when drawing a pyramid of numbers) Generally, the larger an individual organism is, what happens?

Answer 6

the fewer of them there are

Question 7

What is a pyramid of biomass

Answer 7

A pyramid of biomass shows how much mass the creatures at each level would have without including all the water that is in the organisms (their ‘dry mass’

Question 8

Pyramids of biomass are ALWAYS, what?

Answer 8

pyramid-shaped, regardless of what the pyramid of numbers for that food chain looks like

Question 9

Why are Pyramids of Biomass always pyramid-shaped?

Answer 9

because the mass of organisms has to decrease as you go up a food chain – if we take our first food chain as an example, it’s impossible to have 10kg of grass-feeding 50kg of voles feeding 100kg of barn owls

Question 10

What are Pyramids of Energy

Answer 10

Pyramids of energy illustrate the amount of energy contained within the biomass of individuals within different trophic levels

Question 11

The area of each box represents the quantity, what?

Answer 11

energy present

Question 12

Pyramids of energy always have a what?

Answer 12

wide base (due to the large amount of energy contained within the biomass of producers)

Question 13

As you move up the pyramid to higher trophic levels the quantity of energy decreases, why?

Answer 13

as not all energy is transferred to the biomass of the next trophic level (roughly only 10 % of the energy is passed on)

Question 14

Exam Tip

Answer 14

Remember that pyramids of biomass are ALWAYS pyramid-shaped, so they are simple to draw, but pyramids of number can be any shape – so make sure you learn the rules for drawing a pyramid of numbers

Question 15

Energy flows from the sun to the first trophic level (producers) in the form of, what?

Answer 15

light

Question 16

Producers convert light energy into. what?

Answer 16

chemical energy

• This occurs during photosynthesis, when producers convert carbon dioxide and water into glucose and oxygen

Question 17

Producers use this glucose (during respiration) to produce, what?

Answer 17

their own biomass

• Biomass is a store of chemical energy

Question 18

When primary consumers consume (eat) producers, what do they break down?

Answer 18

they break down the biomass of the producer (digestion) and use the chemical energy to increase or sustain their own biomass

Question 19

When secondary consumers consume (eat) primary consumers, what do they break down?

Answer 19

they break down the biomass of the primary consumer (digestion) and use the chemical energy to increase or sustain their own biomass, and so on

Question 20

as chemical energy is transferred from one trophic level to the next, what else is transferred?

Answer 20

biomass is also transferred

Question 21

What is not all transferred from one trophic level to the next?

Answer 21

Not all energy is transferred

Question 22

Approximately how much energy of each trophic level is passed on to the next?

Answer 22

Approximately, only 10%

Question 23

Why are food chains rarely made up of more than six trophic levels?

Answer 23

the total amount of energy available eventually becomes too small to support another trophic level

Question 24

Losses of energy are due to, what?

Answer 24

1. Organisms rarely eat every part of the organism they are consuming – some of the biological material of plants and animals may be inedible

• Carbon dioxide and water are waste products of respiration
• Water and urea are the waste products in the urine, which is produced when proteins are broken down

Question 25

You may be asked to calculate the efficiency of energy and biomass transfers between trophic levels using percentages, how do you do it?

Answer 25

Percentage Efficiency Transfer = Biomass in Higher Trophic Level (Level 2) / Biomass in Lower Trophic Level (Level 1) x 100. IE

Clover (1450) - Snail (138)

138/1450 x 100 = 9.52%