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B4 Key facts sheet
A: Ecology in the local environment (Higher in bold)
Test Mark:
Key Fact
The distribution of organisms within a habitat is affected by the presence of other living
organisms as well as physical factors.
Biodiversity is the variety of different species living in a habitat.
Native woodlands and lakes are natural ecosystems and forestry plantations and fish farms
are artificial ecosystems.
You can map the distribution of organisms in a habitat using a transect line and use Kite
diagrams to show the distribution of organisms.
The differences between:
• an ecosystem includes all the living things in an area and the physical conditions and a
habitat is where an organism lives
• a community is all the living organisms in an ecosystem and a population is a group of the
same species living in the same place.
The biodiversity of natural ecosystems tends to be larger than artificial ecosystems. Can you
compare native woodlands and lakes with forestry plantations and fish farms.
Zonation is a gradual change in the distribution of species across a habitat.
A gradual change of an abiotic factor can result in the zonation of organisms in a habitat.
An ecosystem can be described as self supporting in that it contains everything it needs to
maintain itself (e.g. water and nutrients), than an energy source.
The biodiversity of native woodlands and lakes is greater than forestry plantations and fish
farms because, they maintain themselves without any interference by humans.
Collecting/counting methods:
• pooters are used to suck up small insects so they can be counted and identified
• nets are used to capture animals like butterflies so they can be counted and identified
• pit-fall traps are used to capture crawling insects so they can be counted and identified
• quadrats are used to count the number of species within the frames.
A method to show the variety of plants and animals living in a small area. Count the number of
organisms in a 1m quadrat and multiply the number of organisms by the total area of the
quadrat.
Keys are used to identify plants and animals.
The effect of sample size on the accuracy of an estimate of population size is that the
bigger the sample the more accurate the estimate.
You can estimate of the population size based on:
• the use of capture-recapture data, given the formula:
population size =
number in 1st sample x number in 2nd sample
number in 2nd sample previously marked
You need to make certain assumptions when using capture-recapture data:
• no death, immigration or emigration
• identical sampling methods
• marking not affecting survival rate.
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B4 Key facts sheet
B: Photosynthesis (Higher in bold)
Key Fact
The word equation for photosynthesis:
(light energy)
carbon dioxide + water → glucose + oxygen
(chlorophyll)
Oxygen is a waste product in this reaction.
The balanced symbol equation for photosynthesis:
(light energy)
6CO2 + 6H2O →C6H12O6 + 6O2
(chlorophyll)
The knowledge of process of photosynthesis has developed over time:
• Greek scientists thought that plants gained mass only by taking in minerals from the soil
• Van Helmont’s experiment concluded that plant growth cannot be solely due to nutrients
from the soil
• Priestley’s experiment showed that oxygen is produced by plants.
Experiments using isotopes have increased our understanding of photosynthesis by showing
that oxygen produced by photosynthesis comes from the water and not the carbon dioxide.
Photosynthesis is a two stage process:
• light energy is used to split water, releasing oxygen gas and hydrogen ions
• carbon dioxide gas combines with the hydrogen to make glucose and water.
Plants grow faster in the summer because of more:
• light
• warmth.
Photosynthesis can be increased by providing:
• more carbon dioxide
• more light
• higher temperature.
Limiting factors affect the rate of photosynthesis:
• CO2 is one of the raw materials, the more there is the faster the rate, CO2 is often the
factor that is in the shortest supply so it can limit the rate of photosynthesis
• light provides the energy, so the more light the faster the rate
• temperature affects how quickly enzymes work, so the higher the temperature the faster
the rate, until the enzymes become denatured.
The factor that is in the shortest supply will limit the rate of photosynthesis.
Glucose made in photosynthesis is transported as soluble sugars but is stored as insoluble
starch.
Plants carry out respiration all the time because they need energy all the time.
Glucose and starch are converted to other substances in plants:
• glucose for energy (respiration)
• cellulose for cell walls
• proteins for growth and repair
• starch, fats and oils for storage.
Insoluble substances such as starch are used for storage because:
• it does not move away in solution from storage areas
• it does not affect water concentration inside cells.
Plants take in carbon dioxide and give out oxygen during the day and do
the reverse at night, because they carry out photosynthesis during the day and respiration
all of the time.
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B4 Key facts sheet
C: Leaves and photosynthesis (Higher in bold)
Test Mark:
Key Fact
Chloroplasts are not found in all plant cells.
Chlorophyll pigments in chloroplasts absorb light energy for photosynthesis.
The entry points of materials required for photosynthesis:
• water through root hairs
• carbon dioxide through stomata.
The exit point of materials produced in photosynthesis:
• oxygen through stomata.
Broader leaves enable more sunlight to be absorbed.
Name and locate the parts of a leaf:
• cuticle
• upper and lower epidermis
• palisade and spongy mesophyll layers
• stomata and guard cells
• vascular bundle.
Leaves are adapted for efficient photosynthesis:
• broad so large surface area
• thin so short distance for gases to diffuse
• contain chlorophyll and other pigments to absorb light from different parts of
spectrum
• have a network of vascular bundles for support and transport
• guard cells which open and close the stomata.
• contain chlorophyll and other pigments to absorb light from different parts of
spectrum
The cellular structure of a leaf is adapted for efficient photosynthesis:
• epidermis is transparent
• palisade layer at the top containing most of the chloroplasts
• air spaces in the spongy mesophyll allow diffusion between stomata and
photosynthesising cells
• internal surface area/volume ratio very large.
Plants have several photosynthetic pigments (chlorophyll a and b, carotene and
xanthophyll) this means that they can absorb light across a greater range of colour
wavelengths and so maximise the use of energy from the Sun.
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B4 Key facts sheet
D: Diffusion and osmosis (Higher in bold)
Test Mark:
Key Fact
Molecules enter and leave cells by diffusion through the cell membrane.
Diffusion is the movement of a substance from a region of high to low concentration.
The net movement of particles by diffusion from an area of high concentration to an
area of low concentration, occurs as a consequence of the random movement of
individual particles.
The rate of diffusion is increased by:
• a shorter distance
• a greater concentration difference (gradient)
• a greater surface area.
Water moves in and out of plant cells by osmosis through the cell membrane.
Osmosis is a type of diffusion.
Osmosis is the movement of water across a partially-permeable membrane from an
area of high water concentration (ie dilute solution) to an area of low water
concentration (ie concentrated solution).
Partially-permeable means that only some molecules can pass through.
The net movement of water molecules by osmosis from an area of high water
concentration to an area of low water concentration across a partially-permeable
membrane is a consequence of the random movement of individual particles.
The plant cell wall provides support.
The lack of water can cause plants to droop (wilt).
Carbon dioxide and oxygen diffuse in and out of plants through the leaves.
Water moves in and out of animal cells through the cell membrane.
Plants are supported by the turgor pressure within cells, this is water pressure acting
against inelastic cell wall. Wilting occurs when then is a lack of water and hence a
lack of turgor pressure.
Leaves are adapted to increase the rate of diffusion of carbon dioxide and oxygen by
being thin and having a large surface area for exchange.
When water moves out of a plant cell it becomes flaccid.
Eventually the cell contents collapse away from the cell wall, the cell is plasmolysed.
As turgor pressure increases a plant cell becomes turgid.
The effects of water uptake and loss on plant and animal cells are different because
a cell wall prevents plant cells from bursting.
When an animal cell shrinks due to water loss it becomes crenated.
Animal cells undergo lysis when water moves in, the cell bursts.
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B4 Key facts sheet
E: Transport in plants (Higher in bold)
Test Mark:
Key Fact
Healthy plants must balance water loss with water uptake.
Xylem and phloem in a dicotyledonous root, stem and leaf are arranged in vascular bundles.
The xylem is always on the inside of the phloem.
The function of xylem and phloem:
• xylem - transpiration - movement of water and minerals from the roots to the shoot and
leaves
• phloem - translocation - movement of food substances (sugars) up and down stems to
growing and storage tissues.
Both the xylem and phloem form continuous systems in leaves, stems and roots.
Structure of xylem and phloem:
• xylem vessels - thick strengthened cellulose cell wall with a hollow lumen (dead cells)
• phloem – columns of living cells.
Describe how water travels through a plant:
• absorption from soil through root hairs
• transport through the plant, up the stem to the leaves
• evaporation from the leaves (transpiration).
Experiments can be carried out to show that transpiration rate is affected by:
• light intensity
• temperature
• air movement
• humidity.
Transpiration is the evaporation and diffusion of water from inside leaves.
Transpiration causes water to be moved up xylem vessels because as water evaporates from
the leaves more water is drawn up the xylem to replace it.
The effect on transpiration rate of:
• increase in light intensity means the rate is faster
• increase in temperature means the rate is faster
• increase in air movement means the rate is faster
• decrease in humidity means the rate is faster
Transpiration rate is increased by:
• an increase in light intensity increases rate because more stomata are open for
photosynthesis
• increase in temperature increases rate because water particles have more kinetic energy
and move faster
• increase in air movement increases rate because this keeps a lower concentration of water
outside the leaf
• decrease in humidity increases rate because this keeps a lower concentration of water
outside the leaf
The structure of a leaf is adapted to reduce excessive water loss:
• waxy cuticle
• small number of stomata on upper surface.
The cellular structure of a leaf is adapted to reduce water loss:
• changes in guard cell turgidity (due to light intensity and availability of water) to regulate
stomatal apertures
• number, distribution, position and size of stomata (more on underside of leaf)
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B4 Key facts sheet
F: Plants need minerals (Higher in bold)
Test Mark:
Key Fact
Fertilisers contain minerals such as nitrates, phosphates, potassium and magnesium
compounds and that these are needed for plant growth.
NPK values show the relative proportions of nitrates, phosphates and potassium in fertilisers.
Plants require:
• nitrates for proteins which are needed for cell growth
• phosphates for respiration and growth
• potassium compounds for respiration and photosynthesis
• magnesium compounds for photosynthesis.
Elements obtained from soil minerals are used in the production of compounds in plants:
• nitrogen to make amino acids
• phosphorus to make DNA and cell membranes
• potassium to help enzymes (in photosynthesis and respiration)
• magnesium to make chlorophyll.
Experiments to show the effects on plants of mineral deficiencies can be carried out by:
• using soil-less culture
• each trial missing one mineral.
Minerals are absorbed by:
• being dissolved in solution
• taken by the root hairs from the soil.
Mineral deficiencies that result poor plant growth:
• nitrate – poor growth and yellow leaves
• phosphate – poor root growth and discoloured leaves
• potassium – poor flower and fruit growth and discoloured leaves
• magnesium – yellow leaves.
Minerals are usually present in soil in quite low concentrations.
Minerals are taken up into root hair cells by active transport.
Active transport can move substances from low concentrations to high concentrations
(against the concentration gradient) across a cell membrane, using energy from respiration.
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B4 Key facts sheet
G: Decay (Higher in bold)
Key Fact
The key factors in the process of decay:
• presence of microorganisms • temperature
• oxygen
• moisture.
Decay is important for plant growth because it releases elements back into the environment
for plants to use.
Microorganisms are used to:
• break down human waste (sewage)
• break down plant waste (compost).
Food preservation techniques reduce the rate of decay:
• canning
• cooling
• freezing
• drying
• adding salt/sugar
• adding vinegar.
The rate of decay can be changed by:
• temperature (at warmer temperatures the rate is faster)
• amount of oxygen (the more oxygen the faster the rate)
• amount of water (in moist conditions the rate is faster)
Detritivores including earthworm, maggots and woodlice feed on dead and decaying material
(detritus)
Detritivores increase the rate of decay by producing a larger surface area.
Food preservation methods reduce the rate of decay by:
• canning (heated to kill and sealed to prevent oxygen)
• cooling (slows down reproduction of microbes)
• freezing (microbes stop reproducing)
• drying (removes water, microbes cannot grow)
• adding salt/sugar (causes water to be drawn out of microbes by osmosis, it kills them)
• adding vinegar (vinegar is acid, it kills the microbes)
Lowering the temperature and the amounts of oxygen and water affect the rate of decay
because:
• microbial respiration is slowed down so growth and reproduction of microorganisms slows or
stops.
Saprophytic fungi digest dead material in terms of extracellular digestion. They release
enzymes into their surroundings and absorb the digested chemicals.
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B4 Key facts sheet
H: Farming (Higher in bold)
Key Fact
Farmers can produce more food if they use pesticides but these practices, but these
practices can cause harm to the environment and to health.
Pesticides kill pests which are any organisms that damage crops.
Examples of pesticides:
• insecticides to kill insects
• fungicides to kill fungi
• herbicides to kill plants (weeds).
The disadvantages of using pesticides:
• pesticides may enter and accumulate in food chains
• pesticides may harm organisms which are not pests
• some pesticides are persistent.
Intensive farming means trying to produce as much food as possible from the land, plants and
animals available.
Intensive farming that methods can increase productivity:
• fish farming
• glasshouses
• hydroponics (growing plants without soil)
• battery farming.
Possible uses of hydroponics include:
• glasshouse tomatoes
• plant growth in areas of barren soil.
Intensive farming methods may be efficient but they raise ethical dilemmas.
The advantages and disadvantages of hydroponics:
• better control of mineral levels and disease
• lack of support for plant
• required addition of fertilisers.
Organic farming methods include:
• no artificial fertilisers
• no pesticides.
Pests can be controlled biologically by introducing predators.
Organic farming techniques:
• use animal manure and compost
• crop rotation, including use of nitrogen-fixing crops
• weeding
• varying seed planting times.
Advantages and disadvantages of organic farming techniques:
• organic farming isbetter for the environment because it uses fewer chemicals and causes
less pollution, the treatment of animals follows ethical guidelines
• organic farming takes up more space, is more labour intensive which provides more jobs but
makes it more expensive.
Advantages and disadvantages of biological control, include:
• advantages: no need for chemical pesticides, does not need repeated treatment
• disadvantages: predator may not eat pest, may eat useful species, may increase out of
control, may not stay in the area where it is needed.
Intensive food production improves the efficiency of energy transfer by reducing energy
transfer:
• to pests, including competing plants (weeds)
• as heat from farm animals by keeping them penned indoors (battery farming) so that they
are warm and move around less.
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