B2 REVISION CARDS

YEAST IS A SINGLE-CELLED ORGANISM 

Yeast is a microorganism.  A yeast call has a nucleus, cytoplasm and a cell membrane surrounded by a cell wall

BACTERIAL CELLS HAVE NO NUCLEUS 

Bacteria are also single-celled microorganism 

1) A bacterial cell has cytoplasm and a cell membrane surrounded by a cell wall 

2) The genetic material floats in the cytoplasm because bacterial cells don't have a nucleus 

DON'T BE PUT OFF BY THE FANCY WORD

DIFFUSION IS THE THE SPREADING OUT OF PARTICLES FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION 

It's just the gradual movement of particles from places where they are lots of them to places where they are fewer of them. 

DIFFUSION HAPPENS IN FLUIDS  (AS THESE PARTICLES ARE FREE TO MOVE)

The bigger the difference in concentration, the faster the diffusion rate

CELL MEMBRANE ARE KIND OF CLEVER 

They are clever because they hold the cell BUT they control what goes in and out too 

Dissolved substances can move in and out of cells by diffusion 

Only very small molecules can diffuse through cell membranes (e.g amino acids, glucose, water and oxygen)

particles move through the cell membrane from where there's a high concentration to where there is a low concentration 

EXAMPLES:

PALISADE LEAF CELL ARE ADAPTED FOR PHOTOSYNTHESIS

They are packed with chloroplasts for photosynthesis. More of them at the top of the cell so they are nearer the light 

Tall shape means a lot of surface area exposed down the side for absorbing CO2 from the air in the leaf 

Thin shape means that you can pack loads of them in at the top of a leaf

Palisade leaf cells are grouped together at the top of the leaf where most of the photosynthesis happens 

GUARD CELLS ARE ADAPTED TO OPEN AND CLOSE PORES

Special kideny shape which opens and close the stomata (pores) in a leaf

When the plant has lots of water and the guard cells fills with it and go plump and turgid. This makes the stomata open so gases can be exchanged for photosynthesis 

When the plant is short of water, the guard cells lose water and become flaccid making the stomata close. This helps stop too much water vapour escaping 

Thin outer walls and thickened inner walls make the opening and closing work 

They're also senstive to light and close at night to save water without losing out on photosynthesis.

They are adapted because they allow gas exchange while contolling water loss withing a leaf

RED BLOOD CELLS ARE ADAPTED TO CARRY OXYGEN 

Concave shape gives a big surface area for absorbing oxygen. Also helps them pass smoothly through capillaries to reach body cells. 

They're packed with haemoglobin- the pigment that absorbs the oxygen 

They have no nucleus, to leave more room for haemoglobin 

SPERM AND EGG CELLS ARE SPECIALISED FOR REPRODUCTION 

The main functions of an egg cell are to carry female DNA and to nourish the developing embryo in the early stages. The egg contains huge food reserves to feed the embryo 

When a sperm fuses with an egg, the egg's membrane instantly changes its struture to stop anymore sperm getting in. This makes sure that the off springs ends up with the right amount of DNA 

The function of the sperm is basically to get the male DNA to the female DNA. It has a long tail and a streamlined head to help it swim to the egg. 

There are lots of mitochondria in the cell to provide the energy needed 

Sperm also carry enzymes in their heads to digest through the egg cell membrane.

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

Cytoplasm- gel-like substances where most of the chemical reactions happen 

                (it contains enzymes that control these chemical reactions)

Cell Membrane- holds the cell together and controls what goes in and out 

Mitochondria- there are where most of the reactions for respirations take                         place. Respiartion releases energy that the cell needs 

Ribosomes- these are where proteins are made in the cell

PLANT CELLS HAVE THE SAME WITH A FEW ADDED BITS:

RIGID cell wall- made of cellulose. It supports the cell and strengths it 

Permanent vacuole- contains cell sap a weak solution of sugar and salts 

Chloroplasts- these are where photosynthesis occurs which makes food for the                   plant and contain a substance called chlorophyll