Biology - B4

Habitat - The place where an organism

Community - Populations of different species in a habitat

Population - All the organisms of one species in a habitat

Quadrat

A square frame enclosing a known area. Study a small area within a quadrat and scale up the findings to estimate for larger areas.

1) Count all the organisms in 1m² quadrat

2) Multiply the number of organisms by the total area of the habitat. 

You can calculate the size of the population by using a capture and recapture method.

• Capture a sample of the population and mark the animals in a harmless way
• Release back into environment
• Recapture another sample of the population. Count how many of this sample is marked.
• Estimate population size using this equation:
• Population size = No. in 1st sample x No. in 2nd sample
  • ----------------------------------------------------
  •            No. in 2nd sample marked

The larger the sample size , the more accurate the estimate of the population is likely to be.

Using a Capture and Recapture method assumes:

• There have been no changes in the population size such as deaths, immigration or emigration.  
• Identical sampling methods were used for both populations.
• The marking hasn't affect survival of organisms.

Ecosystems are self supporting

• An ecosystem is all the organisms living in a particular area as well as the non living (abiotic conditions, e.g. temperature, salinity and soil quality)
• Ecosystems are self-supporting - they contain everything they need to maintain themselves. Water, nutrients and essential elements  like carbon.
• The only thing needed from outside the ecosystem in an energy source (normally the Sun)

Distribution is where organism are found within a particular area

• Mark 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.
• If it's difficult to count the individual organisms, you can calculate the percentage cover. (Estimating the area covered)
• Plot the results on a transect in a kite diagram, allowing you to map the distribution of organisms.

Kite diagrams - Show the distribution and abundance of organisms   

Abiotic factors are non-living physical conditions, e.g. light, temperature, water, oxygen, salinity and soil quality.

The distribution of organisms is affected by physical conditions because:

Organisms are adapted to live in certain physical conditions. Meaning they're more likely to survive and reproduce in areas with these conditions.

Many organisms can only survive in the conditions they've adapted to.

Zonation: The gradual change in the distribution of species across a habitat.

A gradual change in abiotic factors leads to zonation. 

Biodiversity: measure of the variety of life in an area

Includes:

1) Amount of variation between individuals of the same species in an area

2) Number of different species in an area

3) Number of different habitats in an area

Biodiversity is important - ecosystems with a high level of biodiversity are healthier than those without - because they are better able to cope with changes in the environment.

• Natural ecosystems: Maintain themselves without interference from humans e.g. native woodlands
• Artificial ecosystems: Created and maintained by humans, e.g. forestry plantations

Native woodlands have a higher biodiversity to forestry plantations

Native woodlands                                                         

• Variety of tree species
• Trees are different ages and size                         
• Variety of plant species                                                
• Variety of habitats                                                         
• Variety of animal species

Forestry plantations

• One species of tree which is planted for timber
• Blocks of trees planted at the same time meaning they're all the same ages
• Fewer variety of plant species because trees are densely planted leaving less room and light for other plants
• Fewer habitats because there aren't enough plant species to create them (when trees are felled, habitats are disturbed and destroyed)
• Fewer animal species because there aren't many habitats or sources of food                                             

Lakes have a higher biodiversity than fish farms

Lakes

• Many different fish species
• Variety of plant species
• Variety of animal species        

Fish Farms

• One species (often non-native) is farmed for food
• Fewer because fish food is added and food waste can cause algal blooms, blocking out sunlight and killing plants
• Fewer animal species because predators are kept out and pests are killed. Also less food and fewer habitats because of lack of plants.     

Photosynthesis uses energy from the Sun to turn carbon dioxide and water into glucose and oxygen. It takes place in the chloroplasts (they contain pigments like chlorophyll that absorb light energy)

6CO₂ + 6H₂O                         C₆H₁₂O₆ + 6O₂

It is a two stage process:

• Water is split up by light energy releasing oxygen gas and hydrogen ions.
• Carbon dioxide gas combines with the hydrogen ions producing glucose and water.

Water IS NOT an overall product (more gets used up in the first stage than made in second stage). 

Glucose is converted into other substances:

• 1) Respiration - Plants use some glucose from respiration, which releases energy so the rest of the glucose can be converted into other useful substances.
• 2) Making cell walls - Glucose is converted into cellulose for making cell walls (particularly in rapidly growing plants)
• 3) Stored in seeds - Glucose is turned into lipids (fats and oils) for storing in seeds. E.g. sunflower seeds contains oil which is used for cooking oil and margarine
• 4) Stored as starch -  Glucose is turned into starch and stored in roots, stems and leaves, ready to use for when photosynthesis doesn't take place (night)
  • Starch is INSOLUBLE, making it good for storing:
    • Can't dissolve in water and move away from storage areas in solution.
    • Doesn't affect the water concentration inside cells (soluble substances would bloat the cells by storing water)
• 5) Making proteins - glucose is combined with nitrates (from soil) to make amino acids and then proteins. They are used for growth and repair. 

Greek scientists, around 350BC, studied plan growth and observed that seeing as plants only touch the soil they must gain mass by taking minerals from the soil.

• Helmont experiment showed plants gained mass by taking in water

In the 1600s, Van Helmont did an investigation with a tree. He measured the soil and the tree and put it in a pot and added rainwater when it was dry. 5 years later he removed the tree from the pot and weighed it to see that it had gained mass immensely. But when weighing the soil there was only a slight change in mass, showing that the gain in mass was from another source. This other source must have been the water he added.

This experiment was important in demonstrating that the plants gain mass from more than one source.

Priestley's experiments showed that plants produce oxygen

• He placed a burning candle in an airtight container, observing that the flame went out and couldn't be re-lit. He then placed a burning candle and a living plant in an air tight container. The flame went out but the after a few weeks, could be re-lit again.
• He concluded that candle was using up something inside the container, making it go out and the living plant restored this air.
• He repeated the experiment with a mouse. When the mouse was placed in the container with the living plant, after a few days, it lasted longer, showing the air was restored.
• Priestly concluded that plants restore something to the air, which we now know is  oxygen.

Oxygen from photosynthesis comes from water

• Scientists released plants release oxygen during photosynthesis but they didn't know whether the oxygen came from the carbon dioxide or water.
• To find out where the oxygen came from, they supplied plants with water containing an isotope of oxygen called oxygen-18. The CO2 the plants got contained normal oxygen-16.
• When the plants photosynthesised, they released oxygen 18, meaning the oxygen came from the water.

Limiting factors control the rate of photosynthesis

• Light - provides energy needed for photosynthesis

If the light is increased, it will increase rate of photosynthesis, but only up to a certain point. After that, it won't make a difference because temperature and/or CO2 will be a limiting factor.

• CO2 - one of the raw materials needed for photosynthesis

CO2 will only increased the rate up to a certain limit. When the graph flattens, CO2 is not the limiting factor. The limiting factors are temperature and light intensity.   

• Temperature - needs to be just right

As the temperature increases, so does the rate, but if the temperature is too high, the plants enzymes will denature, decreasing the rate rapidly.  Enzymes are destroyed at around 45oC.

But, if temperature is a limiting factor, it's too low and things need warming up. 

Diffusion - the net movement of particles from an area of high concentration to an area of low concentration. Happens in liquids AND gases - because the individual particles are free to move randomly. Simplest type is when different gases diffuse through each other.    

Cell membranes

• They hold the cell together but, they let stuff IN AND OUT. Only very small molecules can diffuse through cell membranes - like simple sugars, water or ions. Big molecules, like starch and proteins, can't pass through the membranes.
• In diffusion, particles move randomly (as they go both ways) but, if there's a lot more particles on one side of the membrane, there will be an overall movement from that side.

Rate of diffusion depends on:

• Distance - substances diffuse more quickly over small distances
• Concentration difference (gradient) - If there's a bigger difference in concentration between the particles, diffusion happens faster.
• Surface area - more surface area that is available for molecules to move across, the faster they get from one side to another. 

Photosynthesis

Carbon dioxide + water                      glucose + oxygen

6CO₂ + 6H₂O                    C₆H₁₂O₆ + 6O₂

Respiration

Glucose + oxygen                        Carbon dioxide + water

C₆H₁₂O₆ + 6O₂                   6CO2 + 6H2O

Photosynthesis only happens during the day (when light's available), but plants respire all the time to get energy needed to live.

During the day, plants make more oxygen by photosynthesis than they use in respiration, so in daylight they release oxygen and take in CO2.

At night, plants only respire meaning they take in oxygen and release CO2

Plants exchange gases by diffusion:

Photosynthesis -

When the plant is photosynthesising it used up lots of CO2 so there's very little in the leaf.

This makes more CO2 move into the leaf by diffusion.

As the same time, lots of oxygen is made as a waste product of photosynthesis.

Some is used in respiration and the rest diffuses out of the leaf.

Respiration -

At night, no light means no photosynthesis. Lots of CO2 is made in respiration and lots of oxygen is used up.

There's lots of CO2 in the leaf and little oxygen, meaning CO2 diffuses out and oxygen diffuses in.

Leaves are adapted for photosynthesis and for diffusion:

• They are BROAD, so they have a large surface area for gases to diffuse
• They are THIN, so the CO2 and water vapour only have a small distance to diffuse across to reach the photosynthesising cells.
• The lower surface is full of STOMATA so they let gases such and CO2 and O2 in and out. And also water to escape in transpiration.
• Leaves have GUARD CELLS surrounding each stoma which controls when the stoma opens and closes, allowing the guard cells to control gas exchange.
• There are AIR SPACES in the spongy mesophyll layer which allows CO2 and O2 in and out of cells. There is also a large surface area for gas exchange - 'they have a very big internal surface area to volume ratio'.

Leaves are adapted to absorb light:

• Leaves are BROAD meaning there is a large surface area which is exposed to light.
• Leaves contain lots of chloroplasts, which contain chlorophyll and other photosynthesising pigments to absorb light.
• Different pigments absorb different wavelengths of light so plant cells can absorb most of the Sun's light energy.
• The cells that contain the MOST CHLOROPLASTS are ARRANGED IN THE PALLISADE LAYER at the top f the leaf so they can get the most light.
• The UPPER EPIDERMIS IS TRANSPARENT so that light can easily pass through to the palisade layer.
• Leaves have a network of vascular bundles containing vessels, xylem and phloem. They deliver water and other nutrients to arts of the leaf and take away glucose produced by photosynthesis. They also help support the leaf structure.  

Osmosis - The net movement of water molecules over a partially permeable membrane from a region of higher water concentration to lower water concentration.

Partially permeable membrane - a membrane with small holes so that small molecules such as water, can pass through them and bigger molecules, such as sucrose can't.

Water molecules can actually pass both ways because water molecules can move randomly all the time.

There is a steady net flow into the side with fewer water molecules because there are more molecules on one side. This means the concentrates sucrose solution would get more dilute.

Osmosis is a type of diffusion

When a plant is well watered, the cells draw water by osmosis and become plump and swollen - turgid. The contents of the cell pushes against the inelastic cell wall, causing turgor pressure, which supports the plant tissue.

If there is no water, the plant starts to wilt as the cells lose water, meaning they lose their turgor pressure and become flaccid.

If the plant is really short of water, the cytoplasm inside the cells start to shrink and the cell membrane pulls away from the cell wall. The cell becomes plasmolysed, the plan drooping a bit, but the inelastic cell wall still keeps things in position ensuring the plant doesn't totally lose its shape.

• Plant cells aren't affected by changes in water because they have an inelastic cell wall that keeps everything in place.
• Animal cells don't have a cell wall meaning if it takes in too much water, bursts, known as lysis. If it loses water, it shrivels up, which is known as crenation.
• This means animals have to keep the amount of water in their cells constant, while plants are more tolerant to changes.

Plants have two transport systems - xylem and phloem. Both vessels go to every part of the plant in a continuous system but they're separate.

Phloem - transport food

• Made of columns of living cells with perforated end plates to allow stuff to flow through.
• They transport food substances (sugars) up and down the stem to growing and storage tissues.
• The movement of food substances is known as translocation.

Xylem - takes water UP

• Made of dead cells joined end to end, with no end walls and a lumen down the middle.
• The thick side wall are made of cellulose, which is strong and stiff, giving the plant support.
• They carry water and minerals from the roots to the shoot of the leaves in the transpiration stream. 

Xylem and ploem run alongside each other in vascular bundles.

Roots have to resist crushing as they push through the soil. Xylem is in the CENTRE for strength.

Stems need to resist bending. The xylem FORMS SCAFFOLDING and the phloem is always around the outside of the stem.

In the leaf, xylem and phloem work together and make up a network of veins, which supports the leaves. 

• Roots hairs are the cells onplant roots which grow into long hairs and stick out into the soil.
• Each branch is covered in millions of these microscopic hairs - this gives the plant a big surface area for absorbing water from the soil.
• There's usually a higher concentration of water in the soil that inside the plant, so water is drawn into the cell by osmosis.

Transpiration

Transpiration is caused by evaporation and diffusion of water vapour from inside the leaves.

This creates a shortage of water in the leaf, causing more water to be drawn up through the xylem vessels to replace it.

This means more water is drawn up from the roots and therefore there's a constant transpiration stream through the plant. 

Traspration is a side effect of how plants are adapted for photosynthesis. They have stomata so gases can be echanged easily, but there's more water inside the plant than outside meaning water escapes from the leaves through the stomata.

Benefits of transpiration:

• Constant stream of water keeps the plant cool
• Provides the plant with a constant supply of water for photosynthesis
• The water creates turgor pressure in the plant, supporting the plant,stopping it from wilting.
• Minerals needed by the plants can be brought in by the soil along with water

Transpiration Rate

• Increase in light intensity means a greater transpiration rate as photosynthesis can occur and stomata can open in the light, allowing water to escape.
• Increase in temperature means a greater rate of transpiration as the particles have more energy to evaporate and diffuse out of the stomata.
• Increase in air movement means a greater rate of transpiration. If it's windy, the water vapour which diffuses out is swept away meaning there is a low concentration of water in the air around the leaf. Diffusion then happens quicker 
• Decrease in air humidity means a greater rate of transpiration. If the air is less humid outside the plant, there is a greater concentration difference of water particles, meaning diffusion can occur from an area of high concentration to low concentration. 

Plants adaptations to reduce water loss:

• Leaves have a waxy cuticle covering the upper epidermis, the upper surface is waterproof.
• Most stomata is found on the lower surface where it is darker and cooler, slowing down diffusion to outside the leaf.
• The bigger the stomata the more stomata a leaf has, so the more water the plant will lose. Plants in hot climates have small stomata and fewer of them so they can conserve water and somme have no stomata on the upper epidermis.

Stomata

• Stomata close automatically when supplies of water from roots start to dry up.
• Guard cells have a special kidney shape which open and close the stomata as the guard cells for turgid or flaccid.
• Thin outer walls and thickened inner walls make opening and closing function work properly.
• Open stomata let gases in and out for photosynthesis
• Guard cells are sensitive to light - they open during the day and close at night, allowing them to conserve water without losing out on photosynthesis.

Plants need three main minerals to produce important compounds. They get these elements from the minerals in the soil. If they don't have enough of the minerals, plants suffer deficiency symptoms.

• 1) Nitrates - Contains nitrogen to make amino acids and proteins and are needed for cell growth. If the plans doesn't get enough nitrates, the growth will be poor and will have yellow older leaves.

• 2) Phosphates - Needed for respiration and growth. Contains phosphorus to make DNA and cell membranes. Plants without enough phosphorus have poor root growth and discoloured older leaves (purple).

• 3) Potassium - To help enzymes for photosynthesis and respiration. If there's not enough potassium, plants have poor flower and fruit growth and discoloured leaves.

• Magnesium is also needed in small amounts - it's required for making chlorophyll (for photosynthesis). If there's a deficiency, plants have yellow leaves

Root hairs take in minerals using active transport.

Root hairs give a plants a big surface area for absorbing minerals from the soil.

But, the concentration of minerals in the soil is low and high in the root hair cell.

So normal diffusion can't take place.

Therefore, active transport takes place where it uses energy from respiration and goes against the concentration gradient (low - high) to absorb minerals from the soil.

Living things are made from materials they take from around them.

When they die and decompose, or release materials as waste, the elements are returned to the soil or air around them.

All decomposition is done by microorganisms lie soil bacteria and fungi (decomposers).

The rate of decay depends on:

• Temperature - warm temperature means things decay faster because microorganisms respire faster.
• Amount of water - things decay faster when they are moist because microorganisms need water
• Amount of oxygen (air) - decay is faster when there's more oxygen because microorganisms can respire aerobically, providing more energy.

When these factors are at optimum levels, microorganisms grow and reproduce more quickly, meaning there will be more of them to decay other living things.

Detritivores and saprophytes are both important in decay:

They are grouped according to how they feed.

Detritivores

• Feed on dead and decaying material (detritus).
• This includes earthworms, maggots and woodlice.
• As the feed on decaying material, they break it up into smaller bits, giving it a bigger surface area for smaller decomposers to work on them, speeding up decay.

Saprophytes

• These include fungi.
• Feed on decaying material but they do it by extracellular digestion - they feed by secreting digestive enzymes on the material outside of their cells. The enzymes break down the material into smaller bits, which can be absorbed by the saprophytes. 

Food preservation reduced the rate of decay

1) Canning - puts food in an airtight can, keeping decomposers out

2) Cooling - putting food in the fridge slows the decomposers' reproductive rate.

3) Freezing - putting food in the freezer means decomposers are not able to reproduce due to the low temperatures.

3) Drying - decomposers need water to carry out cell reactions which is prevented.

4) Adding salt/sugar - if there's a high concentration of salt/sugar around decomposers, they'll lose water by osmosis, damaging them and stopping them from working properly.

5) Adding vinegar - vinegar is acidic meaning it kills the decomposers.  

Intensive farming: trying to produce as much food as possible from your land, animals and plants.

Farmers do this in different ways. All the methods involve reducing the energy loss that happens at each stage in the food chain, making the transfer of energy between organisms more efficient.

1) Using herbicides - kills weeds meaning more of the enrgy from the Sun falls on the crops in the field and not to competing plants.

2) Using pesticides - kills insects that eat the crops, ensuring no energy is transferred into a different food chain

3) Batter farming animals - animals are kept close together in small pens so they are warm and can't move around, saving them wasting energy and stops them using up energy to keep warm.

Intensive farming helps to produce a lot of food from less land, meaning a huge variety of top quality food is available all year round, at cheap prices.

Hydroponics: method of intensive farming where plants are grow in nutrient solutions (water and fertilisers) instead of soils.

Hydroponics is usually used to grow glasshouse tomatoes on a commercial scale, as wwell as in areas of barren soil.

Advantages

• Mineral levels can be controlled more accurately
• Diseases can be controlled more effectively

Disadvantages

• Lots of fertilisers need to be added
• There's no soil to anchor the roots and support the plant

1) Removal of hedges to make huge fields destroys the natural habitat of wild creatures and can also lead to serious soil erosion.

2) Careless use of fertiliseres can pollute rivers and lakes through eutrophication.

3) People think that intensive farming of animals such as battery-hens is cruel to animals

4) Pesticides disturb food chains 

• Pesticides disturb food chains

1) Pesticides are sprayed onto crops to kill the pests that damage them, but they can also kill the beneficial organisms.

2) This can cause a shortage of food for animals further up the food chain.

3) Some pesticides are persistent and are hard to get rid of.

4) Pesticides being passed along the food chain is dangerous and can kill animals further up. 

Biological control is using living things instead of chemicals to control a pest.

This means using a predator, parasite or a disease to kill the pest.

For example:

Aphids are pest (because they eat roses and vegetables). Ladybirds are aphid predators so people release them so aphid numbers are controlled.

Certain types of wasps and flies produce larvae which develop on a host insect. The insect then dies. Lots of insect pests have parasites like this.

Myxomatosis is a disease which kills rabbits. It was released in Australia, to control the numbers of rabbits when they were destroying crops.

Advantages

• No chemicals are used meaning there's less pollution and disruptions to the food chains and risk of people eating prayed food.
• No need to repeat the treatment - like with chemicals

Disadvantages

• The predator introduces might not eat the pest
• The predator could eat useful species
• The predator population might rapidly increase and get out of control
• The predator might not stay in the area its needed
• Removing an organism from a food web, whether it be using biological control or pesticide, affects all the other organisms, so you have to be careful.

Alternatives to intensive farming

Organic farming methods

1) Organic fertilisers: animal manure and compost is used. This recycles nutrients left in waste. It's not as good as artificial fertilisers but 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 nutrients from running out (each crop needs different nutrients). Most crop rotations include a nitrogen-fixing crop, such as legume plants. These help put nitrates back in the soil. 

3) Weeding: physically removing the weeds, rather than spraying with herbicides. Is more labour intensive but no chemicals are involved.

4) Varying seed planting times: sowing seeds earlier or later in the season will avoid major pests for that crop, meaning the farmer won't need to use pesticides.

5) Biological control

Advantages

• Use fewer chemicals so less risk of toxic chemicals
• Better for the environment as there's less chance of polluting rivers with fertilisers and using pesticides to disrupt food chains.
• For farming to be organic, they need to follow ethical treatment for animals, meaning no batter farming.

 Disadvantages

• Takes up more space so more land has to be farmland rather than being used for wildlife
• More labour intensive, providing more jobs, but making the food more expensive
• Can't grow as much food
•