Science B4 (OCR Additional science)

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  • Created by: mary
  • Created on: 29-04-12 11:56

Biology - photosynthesis

photosynthesis - the process leaves use to absorbe light and carbon dioxide to provide food (carbohydrate) for growth. 


its function is to absorb light it is addapted to do this this it has a large surface area - to absorbe more light. thin - so theirs a short distance for carbon dioxide to diffuse through into leaf cells. chlorophyl - absorbs sunlight to transfer energy into chicles. veins - support leaf and transfer water and carbohydrates. Stomata - allow carbohydrate to diffuse. 

Epidermis is thin and transparent - allows more light to reach the palisade cells. Thin waxy cuticle - protects  leaf without blocking out light. Palisade cell layer at top of leaf -  absorb more light. Spongy layer - Air spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area. Palisade cells contain many chloroplasts -  absorb all the available light 

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inside the leaf

Shows the waxy cuticle on top of the upper epidermis.Under this is the palisade mesophyll layer and spongy mesophyll layer, which has air spaces in it. At the bottom, is the lower epidermis and wax cuticle. Gases are exchanged through the stoma. On each side of the stoma there is a guard cell with chloroplasts. (

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how plants affect atmosphere

at daytime - the plant is photosynthesising and respiring so Co2 and o2 given out and taken in.

at night - its respiring but not photosynthesising o2 taken in but not given out and co2 is given out but not taken in.

plants always give oxygen out meaning that annimals can breathe  

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Osmosis is the movement of water from a high water concentration to a low water concentration through a partially permeable membrane. Osmosis takes place in all living cells.

Plants absorb water from the soil by osmosis through their root hair cells. Plants use water for several vital processes including photosynthesis and transporting minerals

osmosis in red blood cell --- if palced in water it enters through osmsois. weak membrane means it bursts and pressure in cell increase. cell shrinks in sugrar solution as water moves out via osmosis so the cell is wrinckled. the kidneys make sure this doesnt happen so the concentration of blood is same as cell. 

osmosis in plant cells -- water entering cell by osmosis inlates cell and makes it rigid. loss of water makes it limp and shrinks.  


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plants and water

plants absorbe water from soil through osmosis. root hair cells have large surface area to speed up osmosis. 

water then transported through roots to plant to where its needed. 

  • It's a reactant used in photosynthesis
  • It supports leaves and shoots by keeping the cells rigid
  • It cools the leaves by evaporation
  • It transports dissolved minerals around the plant
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reducing water loss


Plants  in drier conditions have small numbers of tiny stomata only on their lower leaf surface, to save water loss. Most plants regulate the size of stomata with guard cells. Each stoma is surrounded by a pair of sausage-shaped guard cells. In low light the guard cells lose water and become flaccid, causing the stomata to close. They normally only close in the dark when no carbon dioxide is needed for photosynthesis.


Most plant cells are turgid at all times.  supports the weight of the plant, which is important where there is no woody tissue, like leaves, shoot and root tip. If the plant loses water faster than it can be absorbed the cells lose turgor pressure and become flaccid. This causes the plant to wilt.

why sea water kills plants -- sea water contains many chemicals in solution, such as salt. Osmosis will move water across the plant cell membrane, from the weaker to the stronger solution

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transport in plants

Plants 2 types of transport tissue.  Xylem -- transports water and solutes from the roots to the leaves. phloem -- transports food from the leaves to the rest of the plant.

Transpiration -- process which water evaporates from the leaves, resulting in more water being drawn up from the roots.

xylem and phloem 

xylem - transpiration -- water and mineralls from roots to leaves -- collums of hollow dead reinforced cells 

phloem -moves food substances from leaves to other parts of plant -- collums of living cells 

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factors effecting transpiration rate

Factor      Description                     Explanation Light                                  In bright light transpiration increases The stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis Temperature Transpiration is faster in higher temperatures

Evaporation and diffusion are faster at higher temperatures

Wind Transpiration is faster in windy conditions Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf Humidity Transpiration is slower in humid conditions Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air

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minerals in plants

MineralUseDeficiency symptomsExplanation Nitrate ions (NO3) Building proteins and growth Poor growth and yellow leaves All amino acids contain nitrogen. Amino acids are the building blocks of protein. Phosphate ions (PO4) Respiration and growth Poor root growth and discoloured leaves A component of DNA molecules and cell membranes Potassium ions (K+) Respiration and photosynthesis Poor flower and fruit growth, discoloured leaves Must be present for photosynthesis and respiration enzymes to work Magnesium ions (Mg2+) Photosynthesis Yellow leaves Chlorophyll molecules contain magnesium ions. It's the magnesium that makes chlorophyll green.

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i'm not sure if its an accident, but there's no C4 or P4



its good, but there is no c4 or p4



i no sorry, iv not finished it yet, its coming :) 

Allison Burgers


This is the same information as on bbc bitesize, just saying



Allison Burgers wrote:

This is the same information as on bbc bitesize, just saying

well yeah its going to be because its revision for this unit of work so you need to learn the same things, its the same info in all revision resources :L 



Thank you!    For everyone who is confused it is only B4 because it's for the
OCR additional (B4, B5, B6) exam.

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