5.2 Ecosystems rely on energy transfer

Question 1

Phytoplankton

Answer 1

Plankton is a term used to
describe small organisms that are found in the
surface waters of lakes and oceans. Many
planktonic organisms are microscopic algae
which are able to photosynthesise. These
organisms are referred to as phytoplankton. Tiny
planktonic organisms that feed on phytoplankton
make up the zooplankton.

Question 2

Gross primary productivity, GPP

Answer 2

The rate at
which energy is incorporated into organic
molecules by an ecosystem. Some of these
substances, such as glucose, are then broken
down in respiration. The rest are incorporated
into new cells and tissues and become plant
biomass. This is called net primary
productivity. The relationship between gross
primary productivity, net primary productivity
and respiration is given by the equation: gross
primary productivity = net primary productivity
+ respiration.

Question 3

Net primary productivity, NPP

Answer 3

The rate at
which energy is transferred into the organic
molecules that make up new plant biomass is
called net primary productivity (NPP). Gross
primary productivity is the rate at which the
energy from sunlight is converted into organic
substances. Some of these substances, such as
glucose, are then broken down in respiration.
The relationship between net primary
productivity, gross primary productivity and
respiration is given by the equation: net primary
productivity = gross primary productivity 
respiration.

Question 4

Autotrophs, Chemosynthetic autotrophs,

Autotrophic

Answer 4

A method of nutrition in which
an organism builds up the organic molecules it
requires from small inorganic molecules such as
carbon dioxide and water. In order to do this, a
source of energy is necessary. In
photoautotrophs, the source of energy is light. In
chemoautotrophs, this energy comes from
another chemical reaction. Autotrophs are the
producers which are at the base of all food
chains.

Question 5

Algal bloom

Answer 5

The rapid growth of a population
of the microscopic freshwater or marine algae
that make up the phytoplankton. Algal blooms
often result from an increase in the concentration
of nitrates or phosphates associated with
pollution.

Question 6

Photosynthesis, Photosynthesise

Answer 6

The process by
which plants and certain other organisms are
able to convert carbon dioxide into
carbohydrates using light energy. Although
photosynthesis can be summarised in a simple
equation: carbon dioxide + water  glucose +
oxygen, it is a much more complex process
consisting of two sets of reactions, the lightdependent
reactions and the light-independent
reactions.

Question 7

Photolysis

Answer 7

The process of splitting water using
light energy to give oxygen, hydrogen ions and
electrons. Photolysis occurs within the thylakoid
space of the chloroplast. The hydrogen is
involved in the light-dependent reactions of
photosynthesis. The electrons replace those that
were emitted from the chlorophyll molecule

Question 8

Light-Dependent reaction

Answer 8

The process by which
ATP and reduced NADP are generated in
photosynthesis using energy from light and
hydrogen from photolysis of water. The waste
product of this reaction is oxygen, which can
either be used in respiration or released into the
atmosphere. The ATP and reduced NADP are
essential for the light-independent reactions in
which carbohydrate is formed.

Question 9

Light-independent reaction

Answer 9

The biochemical
pathway in which carbon dioxide combines with
ribulose bisphosphate and is converted into
carbohydrate in photosynthesis. This pathway
involves a cycle of reactions, the Calvin cycle,
which eventually regenerates ribulose
bisphosphate. The ATP and reduced NADP
produced in the light-dependent reactions are
essential for this pathway.

Question 10

NADP, Reduced NADP

Answer 10

A coenzyme which
plays an important part in photosynthesis. In the
light-dependent reaction, light energy is
absorbed by chlorophyll and generates ATP and
reduced NADP. These two substances are
essential for the light-independent reactions in
which carbohydrate is formed.

Question 11

ATP, Adenosine triphosphate

Answer 11

Adenosine
triphosphate (ATP) is an important molecule
found in all living cells. It is involved in the
transfer of energy. Most of the ATP in a cell is
produced from ADP and phosphate using energy
transferred during the process of respiration.
When ATP is broken down, ADP and phosphate
are produced and a small amount of energy is
made available. This energy may be used: in
active transport; to synthesise large molecules
such as proteins from smaller ones such as amino acids; and for movement in cells such as
sperm and muscle cells.

Question 12

Chloroplast, Chloroplasts

Answer 12

A chlorophyllcontaining
organelle found in the cells of plants
and certain other organisms such as algae.
Photosynthesis, the process in which light
energy is converted to chemical energy, takes
place inside chloroplasts.

Question 13

Palisade mesophyll

Answer 13

There are two types of
mesophyll found in leaves. Palisade mesophyll
cells are tall, thin cells found near the upper
surface of a leaf. They contain many
chloroplasts and are an important site of
photosynthesis. Underneath the palisade
mesophyll cells is the spongy mesophyll. This
consists of irregularly shaped cells between
which are large air spaces.

Question 14

Thylakoid membranes

Answer 14

A system of
interconnected membrane-bound sacs found
inside a chloroplast. The thylakoids are often
stacked to form grana. Photosynthetic pigments
and electron carriers are embedded in the
thylakoid membranes. Thylakoids are involved
in the light-dependent reactions of
photosynthesis.

Question 15

Thylakoid space

Answer 15

Fluid within the thylakoid membrane sacs contains enzymes for photolysis

Question 16

Outer membrane (chloroplast)

Answer 16

Freely permeable to molecules such as CO2 and H2O

Question 17

Inner membrane (chloroplast)

Answer 17

contains many transporter molecules. These are membrane proteins which regulate the passage of substances in and out of the chloroplast. These substances include sugars and proteins synthesised in the cytoplasm of the cell but used within the chloroplast. The inner and outer chloroplast membrane forms and envelope.

Question 18

Granum, grana

Answer 18

A stack of thylakoid

membranes found inside a chloroplast.

Question 19

Starch grain

Answer 19

stores the product of photosynthesis

Question 20

Stroma

Answer 20

The fluid surrounding the thylakoid
membranes in a chloroplast. The stroma
contains the enzymes which carry out the lightindependent
reactions of photosynthesis.

Question 21

Dna loop

Answer 21

chloroplasts contain genes for some of their proteins

Question 22

Photosystem, PSI, PSII

Answer 22

A group of proteins and
photosynthetic pigments embedded in the
thylakoid membrane of chloroplasts. Several
hundred molecules form a complex that sits in
the membrane and protrudes above and below it.
The energy of the photons absorbed by the
pigments is transferred to a chlorophyll molecule
at the centre of the complex.

Question 23

Electron carrier

Answer 23

A molecule that passes
electrons along an electron transport chain.
The electrons pass from one carrier to the next in
a series of oxidation and reduction reactions,
releasing energy in the process. This energy is
used to produce ATP. Electron carriers are
important in both photosynthesis and
respiration.

Question 24

Electron transport chain

Answer 24

A series of electron
carrier molecules along which electrons are
passed in a series of oxidation and reduction
reactions, releasing energy in the process. This
energy is used to produce ATP. Electron
transport chains are important in both
photosynthesis and respiration.

Question 25

Photophosphorylation

Answer 25

The synthesis of ATP
from ADP and inorganic phosphate using energy
from light.

Question 26

Nucleotide, Mononucleotide

Answer 26

Nucleic acids are
polymers made up from a number of
nucleotides joined to each other by condensation. Each nucleotide has three
components: a five-carbon or pentose sugar
ribose in RNA and deoxyribose in DNA; a
phosphate group; a nucleotide base.

Question 27

ADP, Adenosine diphosphate

Answer 27

A substance
found in all living cells where it is involved in
the transfer of energy. Adenosine diphosphate
(ADP) is produced when a phosphate group is
removed from ATP; energy is released. In this
way energy is transferred and made available for
movement, active transport and the synthesis
of large molecules.

Question 28

ATPase

Answer 28

An enzyme that catalyses the breakdown
of ATP to ADP and phosphate, releasing energy
in the process. An ATPase is very important in
bringing about muscle contraction.

Question 29

Calvin cycle

Answer 29

A biochemical cycle forming part of
the light-independent reactions of
photosynthesis. The Calvin cycle consists of a
series of reactions in which the 5-carbon
compound, ribulose bisphosphate combines
with carbon dioxide to form
glycerate 3-phosphate (GP) and then
glyceraldehyde 3-phosphate (GALP). Some of
the glyceraldehyde 3-phosphate is involved in
the formation of carbohydrates. The rest
completes the Calvin cycle by regenerating
ribulose bisphosphate.

Question 30

Ribulose bisphosphate, RuBP

Answer 30

A five-carbon
compound which combines with carbon dioxide
in the Calvin cycle, the light-independent
reaction of photosynthesis. The six-carbon
molecules formed break down to form glycerate
3-phosphate and this is converted into
glyceraldehyde 3-phosphate. Some of the
glyceraldehyde 3-phosphate is involved in the
formation of carbohydrates. The rest completes
the Calvin cycle by regenerating ribulose
bisphosphate.

Question 31

Ribulose bisphosphate carboxylase, RuBISCO

Answer 31

The enzyme that catalyses the reaction in which
ribulose bisphosphate combines with carbon
dioxide. This reaction is a key part of the lightindependent
reaction in photosynthesis.

Question 32

Glycerate 3-phosphate, GP

Answer 32

A three-carbon
compound formed as part of the Calvin cycle in
the light-independent reactions of
photosynthesis. Ribulose bisphosphate
combines with carbon dioxide to form an unstable six-carbon compound that immediately
breaks down to form glycerate 3-phosphate.
This is converted to glyceraldehyde 3-
phosphate. Some of the glyceraldehyde 3-
phosphate is involved in the formation of
carbohydrates. The rest completes the Calvin
cycle by regenerating ribulose bisphosphate.

Question 33

Glyceraldehyde 3-phosphate, GALP

Answer 33

A threecarbon
compound formed during the lightindependent
reactions of photosynthesis.
Some of the glyceraldehyde 3-phosphate is
involved in the formation of carbohydrates.
The rest completes the Calvin cycle by
regenerating ribulose bisphosphate. This fivecarbon
compound combines with carbon dioxide
at the start of the cycle.

Question 34

Carbon fixation

Answer 34

The process which converts
inorganic carbon (usually in carbon dioxide)
into carbon compounds in living organisms.
Carbon fixation occurs in the light-independent
reactions of photosynthesis. Some bacteria can
also fix carbon through chemosynthesis.

Question 35

Heterotroph, Heterotrophic

Answer 35

A method of
nutrition in which an organism gains its nutrients
by feeding on other organisms. The complex
organic molecules in its food are broken down
by enzymes into simpler soluble substances
before being built up again to form the complex
organic substances which the organism requires.
Heterotrophs are the consumers in food chains.

Question 36

Primary consumer

Answer 36

An organism that feeds on
plants or other photosynthesising organisms. In
food chains and food webs a primary consumer
is a herbivore. In the food chain: algae > water
flea > stickleback, water fleas are primary
consumers.

Question 37

Secondary consumer, tertiary consumer

Answer 37

An
organism which feeds on animals or other
heterotrophic organisms. In food chains and
food webs a secondary or tertiary consumer is a
carnivore. In the food chain: microscopic algae>
 brine shrimp>  flaming>o  eagle, flamingos
are secondary consumers, and the eagle is the
tertiary consumer.

Question 38

Herbivore

Answer 38

An organism that feeds on plants or
other photosynthesising organisms. Cattle, sheep
and rabbits are herbivores, so are seed-eating
birds such as sparrows, and invertebrates such
as butterflies and snails.

Question 39

Carnivore

Answer 39

An animal that feeds on other animals.
In food chains and food webs a carnivore is a
secondary or tertiary consumer. In the food
chain: nettle plants > nettle aphids > two-spot
ladybirds, the ladybirds are carnivores.

Question 40

Food chain, Food chains, Food web, Food webs

Answer 40

A sequence that represents the way in which
energy is transferred from one organism in a
community to another. An example of a food
chain is: nettle plant  nettle aphid  two-spot
ladybird. The position each species occupies in a
food chain is called its trophic level. Food
chains are linked to each other to form food
webs.

Question 41

Trophic level

Answer 41

The position an organism occupies
in a food chain. For example, in the food chain: microscopic algae > brine shrimp>  flamingo
 eagle, the microscopic algae are the
producers, the brine shrimps are the primary
consumers, the flamingos are the secondary
consumers and the eagle is the top consumer. It
is rare for food chains to have more than five
trophic levels.

Question 42

Detritivore

Answer 42

An animal that feeds on dead
remains. Soil organisms such as earthworms and
woodlice are detritivores. Investigations have
shown that saprobionts like bacteria and fungi
break down dead material much faster if it has
passed through the gut of a detritivore.
Detritivores break up tough tissues. This exposes
a greater surface area for the enzymes produced
by the saprobionts to act upon.

Question 43

Decomposer

Answer 43

A microorganism that lives by
breaking down organic compounds in dead
material and other waste products into carbon
dioxide, water and mineral ions. Decomposers
play a very important part in the cycling of
chemical elements such as carbon.

Question 44

Primary productivity equation

Answer 44

NPP=GPP-R

Question 45

Why is the transfer from producers to primary consumers inefficient?

Answer 45

• not all the available food gets eaten
• some undigested food remains in faeces
• much of the food absorbed by the consumer is used in respiration

Question 46

Limiting factor

Answer 46

A factor that limits the rate of a
process. If the limiting factor is increased, the
process will take place at a faster rate. This
increase in rate does not go on indefinitely.
Eventually the rate levels off as other factors
become limiting. Light intensity and carbon
dioxide concentration are limiting factors for
photosynthesis.

Question 47

Biomass

Answer 47

A term that describes the amount of
living material present. Biomass is usually given
in units such as g m–2 referring to both mass and
the size of a sample.