biological membrane

Question 1

What is the structure of the phospholipid bilayer in the fluid mosaic model?

Answer 1

The phospholipid bilayer consists of hydrophilic phosphate-containing heads facing outwards and hydrophobic fatty acid tails facing inwards.

Question 2

How can hormones move across membranes?

Answer 2

Hormones can move across membranes if they are hydrophobic or fat-soluble, allowing them to dissolve in or diffuse through the phospholipid bilayer.

Question 3

What other molecules can move across the phospholipid bilayer?

Answer 3

Other molecules that can move across include water, oxygen, and carbon dioxide.

Question 4

What happens to pigment leakage at different temperatures?

Answer 4

At lower temperatures, there is little absorbance as the membrane is intact. At higher temperatures, absorbance increases steeply as more pigment leaks out due to membrane damage.

Question 5

What is the width of the plasma membrane?

Answer 5

The plasma membrane has a width of 7nm.

Question 6

What is the composition of the plasma membrane?

Answer 6

The plasma membrane consists of a hydrophobic bilayer of fatty acid tails and contains cholesterol, which regulates membrane fluidity.

Question 7

What are the characteristics of phospholipids?

Answer 7

Phospholipids have hydrophilic (polar) heads and hydrophobic (nonpolar) tails.

Question 8

What does the phospholipid bilayer act as a barrier to?

Answer 8

The phospholipid bilayer acts as a barrier to polar or charged particles, such as mineral ions.

Question 9

How do amoebas expel water?

Answer 9

Amoebas expel water using their contractile vacuole via exocytosis.

Question 10

What is the effect of steeper water potential gradients?

Answer 10

At steeper water potential gradients, water enters or leaves a cell faster.

Question 11

What components make up the cell surface membrane?

Answer 11

The cell surface membrane consists of phospholipids, proteins, glycoproteins, cholesterol, and glycolipids.

Question 12

What do channel proteins allow?

Answer 12

Channel proteins allow small or charged molecules to pass through the membrane.

Question 13

What roles do glycoproteins play in cells?

Answer 13

Glycoproteins can act as antigens, receptors for hormones, and assist in cell adhesion.

Question 14

What is the function of cholesterol in the membrane?

Answer 14

Cholesterol stabilizes the membrane and controls its fluidity and permeability to polar or charged particles.

Question 15

How do charged particles pass through cell membranes?

Answer 15

Charged particles can pass through via facilitated diffusion or active transport using channel or transport proteins.

Question 16

What is osmosis?

Answer 16

Osmosis is the movement of water molecules through a partially permeable membrane down the water potential gradient.

Question 17

What is the significance of compartmentalization in cells?

Answer 17

Compartmentalization allows multiple reaction pathways to occur in different organelles of the same cell.

Question 18

How does salt affect plant cells?

Answer 18

• Salt kills weeds as salt dissolves in water,
• so the external solution has lower water potential than inside the cell, so water moves out of plant cells.
• The cells become dehydrated, so lose turgidity and become flaccid and then plasmolyse, so the plant wilts

Question 19

What is active transport?

Answer 19

Active transport is the movement of substances against the concentration gradient using ATP and transport proteins.

Question 20

What are examples of active transport?

Answer 20

Examples include mineral ions into root hair cells and sucrose out of sieve tubes.

Question 21

What happens to cell membranes at higher temperatures?

Answer 21

At higher temperatures, the membrane structure is disrupted, phospholipids vibrate as more EK, incr in size+ no. of gaps in the membrane between phosphlipids in the bilayer, leading to increased fluidity and denaturation of proteins.

Question 22

How do stained cells behave at higher temperatures?

Answer 22

Stained cells can lose color as the membrane becomes more permeable, releasing stain into the surrounding solution.

Question 23

How does water move through the cell membrane?

Answer 23

Water moves through the cell membrane via the phospholipid bilayer and protein channels.

Question 24

What happens to animal cells in distilled water?

Answer 24

• Cell cytoplasm has a lower WP than distilled water , so water moves in, cannot withstand the pressure
• Animal cells may burst due to increased pressure from water entering the cell by osmosis.

Question 25

How can you prevent animal cells from bursting?

Answer 25

add solute to the water so that the solution has the same or lower water potential than the cell

Question 26

What are the functions of the plasma membrane?

Answer 26

The plasma membrane compartmentalizes organelles, forms vesicles, provides a selectively permeable barrier, and contains receptors.

Question 27

What is required for secretion from cells?

Answer 27

Secretion requires energy for vesicle transport and fusion with the plasma membrane via exocytosis.

Question 28

How do phospholipids form a bilayer?

Answer 28

Phospholipids form a bilayer with hydrophobic tails pointing inwards and hydrophilic heads pointing outwards.

Question 29

What roles do proteins play in the membrane?

Answer 29

Proteins form pores, channels, and carriers for transport and facilitate active transport and diffusion.

Question 30

What effect does freezing have on the plasma membrane?

Answer 30

Freezing damages the plasma membrane, increasing its permeability.

Question 31

Where is cholesterol found in the plasma membrane?

Answer 31

Cholesterol is found inside the bilayer between phospholipids.