B3 - Living together - Food and Ecosystems Flashcards
What are enzymes?
Biological catalysts that the rate of a
chemical reaction go faster without being
permanently altered themselves.
What is the active site of an enzyme?
The region of an enzyme in which a
substrate molecule binds and the
reaction takes place.
Why are enzymes described as having a
‘high specificity’ for their substrate?
Only substrates with a specific,
complementary shape can fit into an
enzyme’s active site.
Describe the ‘lock and key’ model
- The active site of the enzyme and the substrate
come into contact - Substrate binds, enzyme-substrate complex forms
- Substrate converted to products
- Products released from the active site. The active
site is now free to bind to another substrate.
What factors affect the rate of an
enzyme-controlled reaction?
● Temperature
● pH
● Substrate concentration
Explain how increasing temperature
initially affects the rate of an
enzyme-controlled reaction
● As temperature increases molecules have more KE
● Movement of molecules increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
Explain how increasing temperature
above the optimum affects the rate of an
enzyme-controlled reaction
● Temperature increases above the optimum
● Increased vibrations break bonds in enzyme’s structure
● Active site changes shape, the enzyme is denatured
● No more enzyme-substrate complexes can form
● Rate of reaction decreases
Explain how pH affects the rate of an
enzyme-controlled reaction
● Enzymes have an optimum pH
● pH shifts from the optimum
● Bonds in the enzyme’s structure are altered
● Active site changes shape, enzyme is denatured
● Rate of reaction decreases
Explain how substrate concentration
affects the rate of an enzyme-controlled
reaction
● Substrate concentration increases
● Number of substrate molecules in the same volume increases
● Probability of a successful collision increases
● More enzyme-substrate complexes form
● Rate of reaction increases
● Once all active sites become full, the rate of reaction plateaus
What is photosynthesis?
A chemical reaction that takes place inside photosynthetic organisms (e.g. plants, algae) converting light energy into chemical energy
Write the word equation for
photosynthesis
carbon dioxide + water → glucose + oxygen
Write the symbol equation for
photosynthesis
6CO2+ 6H2O → C6H12O6+ 6O2
Why is photosynthesis important?
Photosynthesis produces glucose which has a wide range of uses:
● Used in respiration to release energy
● Converted to starch and stored - starch can be broken down to glucose when the plant requires energy
● Used to make a wide range of organic molecules such as lipids, proteins and other sugars which are used for growth
Where does photosynthesis take place?
Within chloroplasts
What type of reaction is photosynthesis?
An endothermic reaction that takes in
energy (in the form of light)
What is chlorophyll?
A pigment found in chloroplasts that
absorbs light
Describe the two main stages of
photosynthesis
- Chlorophyll absorbs light energy which is used to split water into oxygen gas (a waste product) and hydrogen ions
- Carbon dioxide combines with hydrogen ions to form glucose
What does the first stage of
photosynthesis require?
Light energy
Water, H2O
What are the products of the first stage
of photosynthesis?
Oxygen gas, O2
(O2 is a waste product and is released into the atmosphere)
Hydrogen ions, H+
What does the second stage of
photosynthesis require?
Carbon dioxide gas, CO2
Hydrogen ions, H+
What is produced in the second stage of
photosynthesis?
Glucose, C6H12O6
What factors affect the rate of
photosynthesis?
● Temperature
● Light intensity
● Carbon dioxide concentration
What is a limiting factor?
A variable that limits the rate of a
particular reaction
Explain how temperature affects the rate
of photosynthesis
● Higher temperatures provide more KE for enzymes involved in photosynthesis so the rate increases as temperature rises
● The optimum temperature is usually 25°C
● If the temperature becomes too high (around 45°C) enzymes become denatured and the rate of photosynthesis decreases
Explain how light intensity affects the
rate of photosynthesis
As light intensity increases, the rate of
photosynthesis increases until another
factor (e.g. temperature) becomes
limiting.
How can the effect of light intensity on
the rate of photosynthesis be measured
in the lab?
● Using a light meter
● Using the inverse square law
Why does the rate of photosynthesis
decrease as the distance from a light
source increases?
Light intensity is inversely proportional to the
square of the distance from the light source.
Thus, as the distance increases, light intensity
decreases and the rate of photosynthesis
decreases.
Explain how carbon dioxide
concentration affects the rate of
photosynthesis
As carbon dioxide concentration
increases, the rate of photosynthesis
increases until another factor (e.g. light
intensity) becomes limiting.
What is simple diffusion?
The net movement of molecules from an
area of high concentration to an area of
low concentration down a concentration
gradient
Define osmosis
The net movement of water molecules from
an area of high water concentration to an
area of low water concentration across a
partially permeable membrane
What is active transport?
The movement of molecules across a cell
membrane from an area of low concentration
to an area of high concentration, against the
concentration gradient, using energy
By what process do substances enter
and leave single-celled organisms?
Simple diffusion
Why can’t multicellular organisms rely on
simple diffusion alone?
● Small surface area to volume ratio
● Several layers of tissue too deep to
diffuse through
Why must carbon dioxide be
transported into plants and oxygen be
transported out?
Carbon dioxide is required for
photosynthesis.
Oxygen is a by-product of photosynthesis
so it is released.
How do gases such as oxygen and
carbon dioxide move into and out of
plants?
● Diffuse through stomata on the lower surface of the
leaf and through air-filled spaces within the leaf
● Move between cells via simple diffusion across
partially permeable cell membranes
Why do plants require water?
● Photosynthesis
● Maintenance of structure (turgidity)
● Cooling effect
Why do plants require mineral ions?
For growth e.g. nitrates are required to
produce proteins
How are water and minerals transported
into plants?
● Lower concentration of water in root hair cells than in the soil. Water diffuses down its concentration gradient into root hair cells by osmosis.
● Lower concentration of mineral ions in the soil than in the root. Root hair cells take up mineral ions by active
transport.
Outline how root hair cells are adapted
for the absorption of water and minerals
Plant roots are composed of millions of root hair cells which have:
● Long hairs that extend from the cell body, increasing the surface area for absorption
● Many mitochondria which produce ATP for active transport of mineral ions
Name the two plant transport tissues
Xylem
Phloem
What is the function of the xylem?
Transports water and minerals up the
plant, from the roots to the leaves via the
transpiration stream
Describe how the xylem is adapted to
its function
● Composed of dead cells laid end-to-end to form a long, hollow, continuous column
● No end walls which provides little resistance to the
passage of water
● A thick cell wall, composed of cellulose, is strengthened with lignin to provide support
What is the function of the phloem?
Transports sugars up and down the stem
from photosynthetic tissues (e.g. mature
green leaves) to non-photosynthetic tissues
(e.g. developing seeds) via translocation
What are the two cell types that make up
the phloem?
Sieve tube elements
Companion cells
Describe how the phloem is adapted to
its function
● Sieve tube elements are long, thin cells, laid end-to-end, with perforated end plates to enable the flow of sugars
● Sieve tube elements contain no nucleus and little cytoplasm to allow the unimpeded flow of sugars
● Companion cells contain a dense cytoplasm, nucleus and mitochondria
● They provide energy for metabolic processes in both cell types
What is transpiration?
The loss of water vapour from the parts
of a plant exposed to the air due to
evaporation and diffusion
Describe the process of transpiration
● Water evaporates from the mesophyll cell surfaces and diffuses out of the stomata
● Water molecules (which have cohesive properties) are drawn up the xylem vessels to replace the water that has been lost
● This causes more water molecules to be absorbed from the soil into root hair cells
What are stomata?
Pores found in the lower epidermis of a
leaf that allow gas exchange
What are guard cells?
Specialised cells surrounding the stoma
that change shape to control the size of
the pore
In response to stimuli such as light, the
stomata open. Explain how this happens.
● Stimuli e.g. light
● Potassium ions are actively pumped into guard cells
● Reduces the water concentration in the guard cells
● Water diffuses into the guard cells by osmosis
● Guard cells swell and become turgid
● Bend and draw away from each other, opening the stomata
Describe what happens to the stomata
when potassium ions leave the guard
cells.
● Potassium ions leave the guard cells
● Increases the water concentration in the guard cells
● Water diffuses out of the guard cells by osmosis
● Guard cells become flaccid, closing the stomata
What factors affect the rate of
transpiration? (3)
● Light intensity
● Temperature
● Air movement
Describe how high light intensity affects
the rate of transpiration
● High light intensity, greater number of stomata are open to allow gas exchange for photosynthesis
● As photosynthesis increases, more water is taken up from the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
● Rate of transpiration increases
Describe how low light intensity affects
the rate of transpiration
At a low light intensity, fewer stomata are
open so the rate of transpiration
decreases.
Describe how temperature affects the
rate of transpiration
● Temperature increases
● Water molecules have more KE so diffuse out of the stomata more rapidly
● Photosynthesis also increases so more water is taken up from the soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
● Rate of transpiration increases
Describe how air movement affects the
rate of transpiration
● Air movement increases
● High water concentration gradient maintained between the air spaces in the leaf and atmosphere
● Increased rate of diffusion of water molecules out of the stomata
● Rate of transpiration increases
What is translocation?
The movement of sugars (sucrose,
amino acids etc.) up and down a plant,
from the source to the sink, via the
phloem
Briefly describe the process of
translocation
● Sucrose actively transported into the phloem using ATP
● Water enters the phloem by osmosis
● Sucrose diffuses into surrounding cells followed by water down its concentration gradient
Explain the importance of small
molecules such as sugars, amino acids,
fatty acids and glycerol in the body
They are used to synthesise large organic molecules:
● Amino acids join to form proteins
● Simple sugars join to form larger, more complex sugars
● Fatty acids and glycerol combine to form lipids
Describe how producers gain biomass
● Take in carbon and nitrogen-containing compounds from the environment
● During photosynthesis, carbon is combined with oxygen and hydrogen to
form glucose
● Glucose is converted into small molecules: others sugars, fatty acids,
glycerol and amino acids
● Larger organic molecules are synthesised from small molecules and are
used by the plant to build new structures e.g. cell membranes, organelles
Give some examples of long-chain
carbohydrates and their functions in
organisms
● Cellulose - component of cell walls in plants
● Starch - energy storage in plants
● Glycogen - energy storage in animals
Describe the functions of lipids in
organisms
● Energy storage
● Component of cell membranes
How are amino acids formed from
glucose?
Glucose reacts with nitrate ions from the
soil to form amino acids
Describe how consumers gain biomass
● Ingest large organic molecules from producers or other consumers
● Large organic molecules broken down into smaller, simpler
molecules during digestion
● Small molecules absorbed across the surface of the gut wall
● They are transported to the required cells where large molecules
are resynthesised and used to build biomass in the consumer
Outline the levels of organisation in an
ecosystem
● Individual
● Population
● Community
● Ecosystem
Define population
All organisms of the same species living
with one another in a habitat
Define community
All of the populations of different species
living together in a habitat
Define ecosystem
The community of organisms and
non-living components of an area and
their interactions
Organisms within a community are
described as being ‘interdependent’.
What does this mean?
Organisms are dependent upon each other.
e.g. if the population of producers in a food chain
decreases, there will be an accompanying decline in the
population of primary consumers, secondary consumers
and so on down the food chain.
Give some examples of interdependence
in a community
● Plants depend on pollinators e.g. bees
● Herbivores are dependent on plants
● Animals are dependent on mates
Why is competition important in a
community?
Competition limits population sizes as
organisms must compete for resources.
This can stimulate evolutionary change.
What does a food chain show?
A food chain describes the feeding
relationships between organisms and the
resultant stages of biomass transfer.
Define biomass
The total mass of living material
What are trophic levels?
The stages in a food chain
What do arrows in a food chain
represent?
The direction of biomass transfer
Describe a simple food chain
producer → primary consumer →
secondary consumer → tertiary consumer
Why are producers the first trophic level?
● Producers provide all biomass for the food
chain (via photosynthesis)
● The rest of the food chain involves the transfer
of this biomass.
What does a food web show?
It shows how different food chains are
interlinked and how members of an
ecosystem are interdependent.
What does a pyramid of biomass
represent?
It represents the dry mass of living
material at each trophic level of a food
chain.
Why is a pyramid of biomass almost
always pyramid-shaped?
● Producers (at the bottom of the pyramid) have the
greatest biomass so have the longest bar
● As you move along the food chain (and up the
pyramid) biomass is lost so the bars decrease in
length
Why is biomass lost between each
trophic level in a food chain?
● Glucose is immediately used for respiration in plants
● Respiration to generate heat energy, energy for movement
etc.
● Some parts of organisms are indigestible
● Egestion, excretion
Why are there rarely more than four or
five trophic levels in a food chain?
Above this, there is insufficient energy to
support another breeding population
What is the equation for calculating the
efficiency of biomass transfer between
trophic levels?
Efficiency = Biomss available after transfer/Biomass available before transfer X 100
What does a pyramid of numbers
represent?
It represents the number of organisms at
each trophic level of a food chain.
Why are the carbon and water cycles
important?
● Carbon and water are essential to life
● There is a fixed amount of both carbon
and water on Earth which must be
constantly recycled
Describe the stages of the water cycle
- Energy from the sun evaporates water from bodies of water such as
lakes and oceans. - Transpiration also releases water vapour
- Water vapour rises, cools and condenses forming clouds
- Precipitation occurs
- Water is absorbed by the soil and taken up by roots. Some is used in
photosynthesis or becomes part of the plant, entering the food chain. - Excretion returns water to the soil
- Surface runoff returns to streams, rivers and eventually the sea
Describe the stages of the carbon cycle
- Photosynthesising plants remove CO2
from the atmosphere
- Eating passes carbon compounds along a food chain
- Respiration in plants and animals returns CO2
to the atmosphere
4. Organisms die and decompose. Decomposers (bacteria and fungi)
break down dead material and release CO2
via respiration
5. Combustion of materials (e.g. wood, fossil fuels) releases CO2
What is meant by decomposition?
The breakdown of dead materials into
simpler organic matter
How do decomposers break down dead
matter?
Decomposers release enzymes which
catalyse the breakdown of dead material
into smaller molecules.
What factors affect the rate of
decomposition?
● Oxygen availability
● Temperature
● Water content
Why is oxygen required for
decomposition?
Most decomposers require oxygen for
aerobic respiration
How does the availability of oxygen
affect the rate of decomposition?
● As oxygen levels increase, the rate of
decomposition increases
● As oxygen levels decrease, the rate of
decomposition decreases
Why can decomposition still occur in the
absence of oxygen?
Some decomposers respire anaerobically
*However, the rate of decomposition is slower as
anaerobic respiration produces less energy
How does temperature affect the rate of
decomposition?
Decomposers release enzymes:
● Rate highest at 50°C (optimum temperature for enzymes)
● Lower temperatures, enzymes work too slowly, rate decreases
● High temperatures, enzymes denature, decomposition stops
How does soil water content affect the
rate of decomposition?
Decomposers require water to survive:
● In moist conditions the rate of decomposition is high
● In waterlogged soils there is little oxygen for
respiration so the rate of decomposition decreases
Why does decomposition require water?
Water is required for the secretion of
enzymes and absorption of dissolved
molecules.
How do decomposers in landfill sites
contribute to global warming?
● Landfill sites tend to be oxygen deficient
● Decomposers respire anaerobically, producing methane
● Methane is a greenhouse gas which traps energy in the
atmosphere, raising global temperatures
What are abiotic factors?
Give some examples.
The non-living aspects of an ecosystem
e.g. climate, soil, light intensity, water
quality
Describe how environmental conditions
affect communities
● Environmental conditions e.g. temperature, soil pH, light
intensity affect the abundance and distribution of organisms
within communities
● e.g rising global temperatures have been linked to the
extinction of frog species (their thin skin makes them more
vulnerable to temperature changes)
Describe how toxic chemicals affect
communities
● Toxic chemicals (e.g. pesticides) bioaccumulate in food chains
to deadly concentrations at higher trophic levels, killing tertiary
and quaternary consumers
● Fertilisers that contaminate water sources can cause
eutrophication, killing multiple populations within a community
What are biotic factors?
Give some examples.
The living components of an ecosystem
e.g. plants, animals, bacteria, fungi
Describe how a change in the size of
one population may affect other
populations within a community
● A change in the size of one population in a community affects
the size of other populations
● e.g. if the number of predators decreases, the number of prey
will increase as fewer are killed
● e.g. if the number of prey decreases, the number of predators
will decrease as there will be less food available
Describe how competition affects
communities
● The presence of competitors affects population distribution
and size
● e.g. when grey squirrels were first introduced to the UK
they outcompeted the native red squirrels (for food,
shelter etc.), population size of red squirrels declined
Describe how food availability affects
communities
● Availability of food increases, organisms are more likely to
survive and reproduce so population sizes will increase
● Food becomes less readily available, competition between
organisms will increase and fewer are likely to survive
Describe how new pathogens may affect
communities
If a new pathogen is introduced,
population sizes will decrease as many
organisms will become ill and die.
