B2 notes

parts of cells

nucleus- contains genetic material that controls the activities of the cell

cytoplasm- gel-like substance where most of the chemical reactions happen. Contains enzymes that control the chemical reactions


mitochondria- where most of the reactions for respiration take place

ribosomes- where proteins are made in the cell

cell wall- made of cellulose. supports the cell and strengthens it

chloroplasts- where photosynthesis occurs. contain chlorophyll

permanent vacuole- contains cell sap

specialised cells

yeast- has a nucleus, cytoplasm, cell membrane and a cell wall

bacteria- cell membrane, cytoplasm, cell wall, genetic material

palisade leaf cells-

  • chloroplasts at top near light
  • tall=big surface area to absorb carbon dioxide
  • thin to put lots in at top of leaf

guard cells

  • kidney shape opens and closes the stomata
  • fill with water, go plump, opens stomata for gas exchange
  • lose water, go flaccid, stomata closes
  • thin outer walls, thick inner walls
  • sensitive to light, close at night

red blood cells

  • concave shape=big surface area for absorbing oxygen. also helps to pass smoothly through capillaries
  • packed with haemoglobin
  • have no nucleus

sperm cells

  • carry male DNA to female DNA
  • long tail and streamlined head to swim
  • mitochondria to provide energy
  • enzymes to digest the egg cell membrane

egg cells

  • carry female DNA, nourish developing embryo
  • contains food reserver
  • eggs' membrane changes structure when sperm fuses with egg. stops more sperm getting in


  • the bigger the difference, the faster the diffusion rate
  • dissolved substances can move in and out of cells by diffusion
  • only very small molecules are let through

cell organisation

differentiation- the specialisation of a cell. occurs during the development of a multicellular organism

tissue- a group of similar cells that work together to carry out a particular function

organ- a group of different tissues that work together to perform a certain function

organ system- a group of organs working together to perform a particular function

Plant structure and photosynthesis

parts of leaves

  • mesophyll tissue- where photosynthesis occurs
  • xylem and phloem- transport things
  • epidermal tissue- covers plant

equation for photosynthesis- carbon dioxide + water (sunlight + chlorophyll) = glucose and oxygen

  • photosynthesis produces glucose
  • happens inside the chloroplasts
  • chlorophyll absorbs sunlight, converts carbon dioxide and water into glucose and oxygen
  • happens in leaves of all green plants

1) sunlight beating down on the leaf provides energy

2) chlorophyll contained in chloroplasts

3) water reaches cells via xylem

4) carbon dioxide diffuses into the leaf

rate of photosynthesis

limiting factor- stops photosynthesis from happening faster

at night light = limiting factor

in winter temperature = limiting factor

otherwise carbon dioxide is the limiting factor

1) light provides energy for photosynthesis

2) as the light level is raised, the rate of photosynthesis increases, but only to a certain point

3) beyond that it won't make any difference because then either temperature or carbon dioxide will…


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