cell membrane 2

Question 1

role of plasma membrane?

Answer 1

Roles of the plasma membrane

Separates the cell’s contents from the external environment

Regulates transport of materials into and out of the cell

May contain specific enzymes involved in metabolic pathways

Contains antigens so that the immune system can recognise the cell as being self and not attack it

May release chemical signals to other cells and contains receptors for cell communication and signalling (hormone bind to membrane bound receptors)

May be the site of chemical reactions

Question 2

role of plasma membrane within cells?

Answer 2

The cristae of mitochondria which provides a large surface area for aerobic respiration

The thylakoid of chloroplasts which house chlorophyll and are the site of photosynthesis

The plasma membrane of the epithelial cells of the small intestine which contain digestive enzymes that breakdown certain sugars

Question 3

Explain the neuronal cell membrane?

Answer 3

Protein channels and carriers covering the long axon allow the transport of ions to bring the conduction of electrical impulses along their length

They have a myelin sheath of flattened cells around them several times to give more membrane layers and to insulate the electrical impulses

Question 4

Explain the root hair cell membrane?

Answer 4

They have many carrier proteins which transport nitrate ions from the soil into the cell as part of the nitrogen cycle.

Question 5

Define passive and facilluated diffusion?

Answer 5

Diffusion across membranes

Diffusion – movement of molecules from an area of high concentration of that molecule to an area of low concentration across a partially permeable membrane along a concentration gradient. It is passive and does not involve metabolic energy (ATP)

Facilitated diffusion – the movement of molecules from an area of high concentration of that molecule to an area of low concentration across a partially permeable membrane via protein channels or carriers. This still does not require metabolic energy (ATP)

Passive processes only use the kinetic energy of the molecules, not ATP.

When molecules move down their concentration gradient they are still moving randomly but remain evenly dispersed which is called net diffusion. They have reach equilibrium.

Concentration gradient is maintained by the respiring cells using the O2 in animals and the carbon dioxide diffusing into the palisade cell to be used in chloroplasts for photosynthesis and the constant use of these molecules inside the cell maintains a concentration gradient as there is always a higher concentration in the external environment.

Question 6

Factors the affect the rate of simple diffusion?

Answer 6

Temperature – as this increases, kinetic energy increases so rate of diffusion increases

Diffusion Distance – the thicker the membrane/diffusion distance, the slower the rate of diffusion

Surface area – more diffusion can take place of a larger surface area

Size of diffusing molecule – smaller molecules/ions diffuse more quickly

Concentration gradient – steeper the gradient the faster the diffusion

Neurons have many ion channels at synapses to aid the electrical conductivity between cells.

Epithelial cell membranes always have chloride ion channels as these play a part in regulating mucus composition.