Estimating Population Sizes
1) A population is all the organisms of one species in a habitat
2) Populations of different species in a habitat make up a community
Esitmating Population Sizes
A quadrat is a square frame enclosing a known area.
1) Count all the organisms in a 1m^2 quadrat
2) Multiply the number of organisms by the total area of the habitat
Estimate Population Sizes using Capture-Recapture
To estimate population size using the the capture-recapture method:
1) Capture a sample of the population and mark the animals in a harmless way
2) Release them back into the environment
3) Recapture another sample of the population. Count how many of this sample are marked.
4) Estimate population size using this equation:
Population size= number in first sample x number in second sample
number in second sample previously marked
Ecosystems are Self-Supporting
1) An ecosystem is all the organisms living in a particular area, as well as all the non-living conditions
2) Ecosystems are self supporting because they contain almost everything they need to maintain themselves. e.g water, nutrients
3) The only thing an ecosystem needs is an energy source, e.g the sun
Transects are used to Investigate the Distribution of Organisms
a) You can investigate distribution using lines called transects
b) To do a transect, you mrk out a line using a tape measure and place quadrats next to each other all the way along the line. You then count and record the organisms you find in the quadrats.
Zonation is the gradual change in the distribution of species across a habitat
1) Abiotic factors are all the non-lioving, physical factors in an environment e.g light, temp
2) The distribution of organisms is affected by abiotic factors because:
- Organisms are adapted to live in certain physical conditions.
- Many organisms can only survive in the conditions they're adapted to.
A gradual change in abiotic factors can lead to the zonation of organisms in a habitat. For example, in a coastal habitat, changes in salinity and soil depth result in zones where different types of plants grow,
Biodiversity - a measure of the variety of life in an area
Biodiversity includes:1) The amount f variation between individuals of the same species in an area
2) The number of different species in an area
3) The number of different habitats in an area
Ecosystems with a high level of biodiversity are healthier than those without because they are able to cope with changes in the environment.
Natural Ecosystems have a higher biodiversity than artificial ones
1) Natural ecosystems maintain themselves without any major interference from humans
2) Artificial ecosystems are created and maintained by humans e.g fish farms
E.g Native Woodlands - variety of tree species
Forestry Plantation - one species of tree planted for timber
Photosynthesis is a Two-Stage Process
Equation: 6COv2 + 6Hv2O -------> Cv6Hv12Ov6 + 6Ov2
Glucose is converted into other substance
Uses of glucose:
a) For Respiration
b) Making Cell Walls
c) Stored in Seeds
d) Stored as Starch
5) Making Proteins
1) Greek scientists concluded that plants gain mass from soil minerals
-Van Helmont decided that plants gain mass by taking in water
He only added water to a plant for 5 years and weighed it at the end noticing the increase in mass
- Joseph Priestly experiment showed that plants produce oxygen
a) He placed a burning candle in a sealed container and observed that the flame went out after a short time. The candle couldn't be re-lit while in the container.
b) He then placed a burning candle and a living plant in the container. The flame went out after a short time, but after a few weeks the candle could be re-lit.
3 Limiting Factors that control the rate of photosynthesis
1) Not enough light slows down the rate of photosynthesis
2) Too little carbon dioxide also slows it down
3) The temperature has to be jurst right so that enzymes do not denature
Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration
a) Diffusion happens in both liquids and gases, this is because the individual particles in these substances are free to move about randomly.
Cell membranes hold the cell together but they also let stuff in and outt
1) Only very small molecuels can diffuse
2) The rate of diffusion depends on three main things:
b) Concentration difference
c) Surface Area
Diffusion in Leaves
Plants carry out Photosynthesis and Respiration
1) Photosynthesis and respiration are opposite processes:
Photosynthesis: carbon dioxide + water -> glucose + oxygen ( requires energy )
Respiration: glucose + oxygen -> carbon dioxide + water ( energy released )
2) Photosynthesis happens during the day but plants respire all the time to get the energy they need to live
3) During the day, plants make more oxygen by photosynthesis that they use in respiration.
4) At night though, plants only respire this means they take in oxygen and release carbon dioxide.
Plants Exchange Gases by Diffusion
In photosynthesis lots of carbon dioxide is used up this makes more carbon dioxide moves into the leaf by diffusion. At the same lots of oxygen is being made as a waste product of photosynthesis.
In respiration lots of carbon dioxide is made and lots of oxygen is used up, now carbon dioxide is diffusing out and oxygen diffusing in.
Leaves are Adapted for Photosynthesis
Leaves are Adapted for Diffusion
1) Large surface area
2) Thin meaning carbon dioxide and water vapour only have to diffuse a short distance
3) Stomata allow water to escape - process called transpiration
4) Leaves have guard cells surrounding each stomata to control when the stomata open
5) There are air spaces in the spongy mesophyll layer allowing gases to move between the stomata and photosynthesising cells.
Leaves are Adapted to Absorb Light
1) Large surface area
2) Lots of chloroplasts, contain chlorophyll and other photosynthetic pigments to absorb light energy.
3) Different pigments absorb different wavelengths of light, so plant cells can make thye most of Sun's energy by absorbing as much of it as possible.
4) The cells that contain the most chloroplasts are arranged inthe palisade layer near the top of the leaf so that thy can get the most of the life.
5) The upper epidermis is transparent so the light can pass through to the palisade layer.
Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
1) A partialy permeable membrane is just one with very small holes it in, the water molecules pass both ways through the membrane during osmosis.
2) As there are more water molecules on one side than the other there's a steady flow of water into the region with fewer water molecules.
3) This means the concentrated solution becomes more dilute
4) Osmosis is a type of diffusion.
Turgor Pressure Supports Plant Tissues
a) When a plant is well watered, all its cells will draw water in by osmosis and become plump and swollen. When cells are like this they're said to be turgid.
b) The contents of the cell push against the inelastic cell wall, this is called turgor pressure. Tugor pressure helps support the plant tissues.
c) If there's no water in the soil, a plant starts to wilt, the cells can't get water so they lose their turgor pressure becoming flaccid.
Transport Systems in Plants
Phloem Tubes Transport Food:
1) Made of columns of living cells to allow food to pass through
2) They transport food substances ( mainly sugars ) both up and down the stem to grow and store tissues
3) This movement of food substances around the plant is known as translocation.
Xylem Vessels take Water Up:
1) Made of dead cells joined end to end with no end walls between them and a hole down the middle
2) The thick side walls are made of celulose. They're strong and stiff, which gives the plant support
3) They carry water and minerals from the roots up the shoot to the leaves in the transpiration stream.
Water Flow through Plants
Root Hairs take in water by Osmosis
1) The cells on plant roots grow into long 'hairs' which stick out into the soil.
2) Each branch of a root will be covered in illions of these microscopic hairs.
3) This gives the plant a big surface area for absorbing water from the soil.
4) There's usually a higher concentration of water in the soil than there is inside the plant, so the water is drawn into the root hair cell by osmosis,
Transpiration is the Loss of Water from the plant
1) Transpiration is caused by evaportaion and diffusion of water vapour from inside the leaves.
2) This creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through th xylem vessels.
3) This in turn means more water is drawn up from the roots, and so there's a constant transpiration stream of water through the plant.
Water Flow Through Plants +1
Increasing the Traspiration Rate:
1) Increase the light intensity: the brighter the light the greater the transpiration rate
2) Increase the temperature: The warmer it is, the faster transpiration happens
3) Increase in air movement: if there's lots of air movement around a leaf, transpiration happens faster
4) Decrease in air humidity: if the air around the leaf is very dry, transpiration happens ore quickly.
Plants need to balance water loss with water uptake
Plants are adapted to help reduce water loss from their leaves in the following ways:
1) Leaves usually have a waxy cuticle covering the upper epidermis. This helps make the upper surface of the leaf waterproof.
2) Most stomata are found on the lower surface of a leaf where it's darker and cooler.
3) The bigger the stomata and the more stomata a leaf has, the more water the plant will lose. In hot climates where plants need to conserve water they have fewer and smaller stomata.
Minerals Needed for Healthy Growth
Plants Need Three Main Minerals
1) Nitrates - contain nitrogen for making amino acides and proteins, needed for cell growth
2) Phosphates - needed for respiration and growth, contain phosphorus for making DNA and cell membranes.
3) Potassium - to help enzymes needed for photosynthesis and respiration.
Magnesium is also needed in small amounts: Magnesium is very significant as it's required for making chlorophyll.
Root hairs take in minerals using active transport:
1) Root hairs give the plant a big surface area for absorbing minerals from the soil
2) But the concentration of minerals in the soil is usualy pretty low.
3) Active Transport uses energy from respiration to help the plant pull minerals into the root hair against the concentration gradient.
Decay is due to Microorganisms
1) Living things are made of materials they take from the world around them
2) When they die and decompose, or release material as waste, the elements they contain are returned to the soil or air where they originally came from.
3) Nearly all decomposition is done by microorganisms like soil bacteria and fungi
4) The rate of decay depends on three main things:
a) Temperature - a warm temperature makes things decay faster because it speeds up respiration in microorganisms.
b) Amount of water - things decay faster when they're moist because microorganisms need water
c) Amount of oxygen - decay is faster when there's oxygen available.
Detritivores and Saprophytes feed on decaying material
Detritivores and Saprophytes are both types of organisms that are important in decay. Detritivores feed on dead and decaying material, saprophytes also feed on decaying material.
Intensive Farming is used to produce more food
Intensive farming means trying to produce as much food as possible from your land, animals and plants. Farmers can do this by:
1) Using herbidcides to kill weeds. This means that more of the energy from the Sun falling on fields goes to the crops.
2) Using pesticides to kill insects that eat the crops.
3) Battery farming animals, the animals are kept close together indoors in small pens.
Hydrophonics is where lants are grown without soil
1) Hydrophonics is another method of intensive farming, It's where plants are gorwin in nutrient solutions instead of in soil
2) Hydrophonics is often used to grow glasshouse tomatoes on a commercial scale, as well as to grow plants in areas with barren soil.
3) Advantage: Mineral levels can be controlled more accurately, disadvantage: lots of fertilisers need to be added.
Pesticides and Biological Control
1) Pesticides are sprayed onto crops to kill the creatures that damage them, but unfortuntely they can also kill organisms that aren't pests.
2) This can cause a shortage of food for animals further up the food chain
3) Some pesticides stay in ecosystems and are hard to get rid of
4) There's a danger of pesticides being passed along the food chain and killing the animals further up
You can use biological control instead of pesticides
Biological control means using living things instead of chemicals to control a pest.
e.g Aphids are a pest because they eat roses and vegetables. Ladybirds are aphid predators, so people release them into thier fields and gardens to keep aphid numbers down.
Advantages: No chemicals are used, so there's less pollution, disruption of food chains and risk to people eating the food that's been sprayed.
Disadvantages: the predator that you introduce might not eat the pest aking it useless
the predator could eat useful species
Alternatives to Intensive Farming
Organic Faming Methods
1) Use of organic fertilisers (manure) This recycles the nutrients left in plant and animal waste. It doesn't work as well as artificial fertilisers, but it is better for the environment.
2) Crop rotation - growing a cycle of different crops in a field each year. This stops the pests and diseases of one crop building up and stops the nutrients running out.
3) Weeding - this means physically removing the weeds, rather than just spreaying them with a herbicide.
4) Varying seed planting times - sowing seeds later or earlier in the season will avoid the major pests for that crop
5) Biological control - this is covered on the previous page
Adv and Disadv of Organic Farming Methods
Adv: fewer chemicals, better for the environment
Disadv: takes up more spcae than intensive farming, more labour-intensive