TRANSPORT ACROSS CELL MEMBRANES

Question 1

Diffusion

Answer 1

diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
- down a concentration gradient.
- diffusion is a passive process,no energy is needed.
small and non polar particles can diffuse through the phospholipid bilayer as they are soluble in lipids, so they can dissolve in hydrophobic bilayer.

Question 2

facilitated diffusion

Answer 2

larger molecules such as glucose and amino acids and ions like sodium and chloride can only pass through the membrane with certain proteins which is called facilitated diffusion.

Question 3

carrier protein

Answer 3

• carrier proteins move large molecules across the membrane down a concentration gradient.
• the molecule attatches to the protein in the membrane.
• the protein changes shape and releases the molecule intp the opposite side of the membrane.

Question 4

channel proteins

Answer 4

• channel proteins form pores in the membrane for the particles to diffuse through.
• different channel proteins facilitate diffusion of different charged particles.

Question 5

microvili and diffusion

Answer 5

microvilli increases the surface area, which means more particles can be exchanged in a same amount of time- increases the rate of diffusion.

Question 6

facilitated diffusion depends upon

Answer 6

• the concentration gradient
• number of channel proteins or carrier proteins.

Question 7

osmosis

Answer 7

osmosis is the diffusion of water across a partially permeable membrane from a region of higher water potential to a region of lower water potential.

Question 8

water potential

Answer 8

water potential is the potential of the water molecules to diffuse out or into the solution.
- pure water has the highest water potential.

Question 9

osmosis in plant cells

Answer 9

• when a plant cell is place din a pure water or dilute water solution,water will enter into the cell through its partially permeable cell membrane as the pure water has a higher water potential.
• as water enters vacoule of the cell, the volume increases.
• the expanding protoplast pushes against the cellwall, the inelastic cell wall prevents from bursting.
• the cell becomes turgid

Question 10

plasmolysis

Answer 10

• when a plant cell is placed in a solution with a lower water potential, water leaves the cell through osmosis through its partially permeable cell membrane.
• as water leaves the vacoule, the volume decreases and the protoplast starts to shrink away from the cell wall which is what we call plasmolysis.

Question 11

active transport

Answer 11

• active transport involves carrier proteins. a molecule attatches to the carrier protein, the protein changes shape which moves the molecule across the membrane releasing it on the other side.

Question 12

differences between active transport and facilitated diffusion

Answer 12

• active transport requires energy but facilitated diffusion doesnot.
• active transport moves solutes across the concentration gradient whereas facilitated diffusion moves the solutes down the concentration gradient.

Question 13

energy in active transport

Answer 13

atp is the common source of energy in the cell which is produced by respiration.
- atp undergoes a hydrolysis reaction splitting into adp and pi which releases energy so that the solutes can be transported.

Question 14

co transporters

Answer 14

co-transporters are a type of carrier proteins.
- they bind two molecules at a time.
- the concentration gradient of one molecule is used to move the other molecule against its own concentration gradient.
example is the co transport of sodium ions and glucose

Question 15

factors affecting rate of active transport

Answer 15

1. speed of individual carrier proteins
2. rate of respiration
3. number of carrier proteins present.

Question 16

co-transport in the mammalian ileum

Answer 16

1.sodium ions are actively transported out of the epithelial cells into the bloodstream which then lowers the sodium ion concentration in the epithelial cell.
2. sodium ions can diffuse from the lumen into the epithelial cells down a concentration gradient.
3. the protein the sodium ions diffuses through is a co-transport protein , so either glucose or amino acid is attatched and transported into epithelial cells again the concentration gradient.
- glucose then moves by facilitated diffusion into the blood from the epithelial cells,.

Question 17

note

Answer 17

• glucose concentration is always lower in blood than in the epithelial cells because blood flows and absorbed glucose is carried away