Biology B4

Photosynthesis = 6CO2 + 6H2O + ATP = Glucose + 6O2

  • Occurs in the leaves of plants
  • They obtain CO2 from air and water from soil for photosynthesis; plant uses light energy from the sun to convert CO2 and H2O into food. Chlorophyll allows the water to split intohydrogen ions and O2 gas which then combine to form glucose.
  • Occurs in the chloroplasts  which contain chloropyhll, a green pigment
  • Produces glucose and O2. Glucose is a type of sugar and is used for plant food. O2 is a waste product and diffuses out of the leaves

Advantages of Glucose stored as starch (Iodine is used to test for starch):

Starch can be converted back into glucose for respiration in plant cells

Starch is insoluble and so will not dissolve in water and flow out of the cells when it is stored

Starch doesn't affect the water concentration inside cells

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  • Created by: APriest
  • Created on: 07-04-14 09:24

Rate of Photosynthesis

Day: plants photosynthesise at a faster rate than they respire, taking in more CO2 for photosynthesis and releasing extra O2

Night: resipre but do not photosynthesis. O2 is taken into the leaf and waste CO2 is released

(When the graph levels out, another limiting factor must have occurred).

3 Limiting factors: light, temperature and carbon dioxide

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Diffusion and Osmosis

Stomata: tiny holes on the underside of the leaf that allow gas to enter. They open and close in response to how much water is in the guard cells

Chloroplasts: contain chlorophyll, carotene, xanthophyll. Their jobis to absorb a wide range of wavelengths for photosynthesis to occur

Diffusion: the movement of particles from high to low concentration. The rate of this is affected by concentration, surface area, temperature and distance that they must travel

Solute: thing you dissolve

Solvent: the thing you dissolve in

Solution: the end product after dissolving

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Adaptations of a leaf for photosynthesis:

  • Leaves are broad and flat - large surface area to absorb light
  • Leaves are thin - short diffusion pathway for CO2 to diffuse to mesophyll and palisade cells
  • Cells contain chlorophyll - absorb energy from spectrum
  • Palisade cells - packed in rows to fit more cells in
  • Veins contain vascular bundles - form network to support leaf blade. Carry root water and soluble sugars away
  • Lots of stomata - CO2 in and O2 out
  • Stomata pores in lower epidermis allow CO2 in and O2 out
  • Upper palisade layer which receives most light and contains the most chloroplasts

Osmosis is diffusion of water from high to low concentration from a dilute to a concentrated solution through a permeable membrane

Palisade Cells - paced with chloroplasts; tall shape means a lot of surface area is exposed down the side for absorbing CO2 from the air in the leaf; shape also means a good chance of light hitting a chloroplast

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Turgor Pressure

When a plant is well watered, all its cells draw in water by osmosis, they become plump and swollen (turgid). The contents of the cell push against the cell wall - this is called turgor pressure. This helps to support the plant tissues.

If there is no water in a cell then it wilts. The cells start to lose water as well as their turgor pressure. They become flaccid.

If a plant is really short of water the cytoplasm inside the cell starts to shrink and the membrane pulls away from the cell wall. This is now plasmolysed; however the plant doesn't lose shape because the inelastic cell wall keeps things in position.

Animal cells don't have a cell wall. If an animal cell takes in too much water then it burts. This is known as lysis. If an animal cell loses to much water is shirvels and crenates.

Water flow through plants - root hairs take in water by osmosis. Root hairs give the plant a large surface area for absorbing water from the soil. There is usually a higher concentration of water in the soil than the pant so water is drawn into the root hair cell by osmosis.

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Transpiration is the loss of water from a plant. It is caused by the evaporation and diffusion of water from inside the leaves. This creates a slight shortage of water in the leaf; more water is drawn up from the rest of the plant through the xylem vessels. More water is then drawn up from the roots. There is a constant transpiration stream of water through the plant.

Transpiration is a side effect of the way leaves are adapted for photosynthesis. The stomata are essential for gas exchange but this means that because more water is inside the plant than around it, water escapes from the leaves through the stomata.

Benefits: constant stream keeps the plant cool, constant supply of photosynthesis water for the plant, creates turgor plressure (which prevents wilting and gives support), minerals needed can be brought from soil with the water. What affects it?

Light - brighter=greater the rate. Photosynthesis only happens during day (allow water to evap)

Temp - warmer=greater. Water particles=more energy to evap & diffuse from stomata

Air movement - lots=faster. Diffusion happens faster as water vapour is moved from outside

Humidity - dry=faster. Higher concentration difference= faster rate of diffusion

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Reducing Water Loss

Waxy cuty on upper epidermis; waterproof

Stomata on underside of leaf; darker and cooler= slows down the diffusion of water out of the leaf

Bigger stomata means more water loss.

Phloem Tubes: made from living cells and are perforated (allow substances to pass through), transport food made in leaves to growing tissues. 2 directional transport. Movement of food is translocation.

Xylem Tubes: made of hllow dead cells, give plant support, carry minerals and water from the roots up the transpiration stream. 1 directional transport.

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Minerals in Plants

Nitrates: make amino acids and protein from nitrogen. Needed for cell growth. Lack of them means stunted growth and yellow leaves.

Phosphates: DNA and cell membranes from phosphorus. Needed for respiration and growth. Lack of them means poor growth and purple leaves.

Potassium: helps enzymes needed for photosynthesis and respiration. Lack of them means poor flower and fruit growth and discoloured leaves.

Magnesium: small amounts, needed for making chlorophyll. Necessary for photosynthesis. Lack of them means yellow leaves.

Minerals absorbed by active transport. Root hairs give big surface area for absorbing minerals from the soil. Concentration of minerals in the soil is usually pretty low.

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Energy and material lost from the food chain from egestion (pooing and waste)

Hardly ever food chains with more than 5 trophic levels because not enough energy left

Efficiency = (energy available at next level / energy that was available at previous level) x100

Biomass can be used for fuel. Fast growing trees means that carbon dioxide emissions are balanced as the replacement trees are still removing carbon. Fermenting biomass is breaking down anaerobic respiration to be burned to release energy for heating, powering turbines etc.

Energy can be released by eating it, feeding it to livestock, growing plants seeds and using it as a fuel.

Development of biofuels is good because: they're renewable, they reduce air pollution and there is no acid rain gases produced.

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Intensive Farming

Done trying to produce as much food as posible from land and plants. All methods involve reducing the energy losses that happen at each stage of the food chain. Examples of how its done:

Using herbicides to kill weeds. More energy from the sun falls goes to crops and not any competing plant. Using pesticides to kill the insectsthat eat the crops. This means that no energy is transferred into a different food chain. Animals are battery farmed. They are kept close together in tiny pens meaning that they're warm, can't move about and therefore no energy is wasted in movement or keeping warm.

Negatives: removal of hedges for huge fields destroys natural habitats and creates soil erosion, careless use of fertilisers pollutes rivers and can lead to eutrophication, pesticides can disturb food chains, ethics (animal farming is considered cruel).

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Plants grown without soil. Most tomatoes and cucumbers are grown in nutrient solutions (water and fertiliser) instead of soil.

Adv: take up less space (lesslandrequired), no soil prep or weeding, plants grown in poor soiled areas, no soil pest problems, mineral levels can be easily controlled.

Disadv: expensive to set up and run, specially formulated soluble nutrients need to be used, gorwers need to be skilled / properly trained, plants need support as there is no soil to anchor to.

Organic takes up more room than intensive. More labour intensive and provides more jobs but makes the food more expensive. No as much food can be grown. Organic uses fewer chemicals (less risk of toxic remnants on food).

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Decay - Sterilisation

Sterile:- free from bacteria or other living micro-organisms therefore completely clean.

Temp, moisture and oxygen affect the rate of decay.

Canning - keeps decomposers out

Cooling - slows decay by slowing respiration of micro-organisms down

Freezing - stops micro-organisms from respiring / reproducing

Detrivores: feed on dead, decaying matter. Break down decaying matter into smaller pieces giving a bigger surface area for the smaller decomoposers to work on and speeds up decay

Saprophytes: feed on decaying matter by extracellular digestion. They secrete their enzyes onto the material ouside of their cells. The enzymmes break down the material into smaller pieces which can then be absorbed by the saprophyte.

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