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WJEC AS Biology > Cell Membranes & Transport- Unit 1.3 > Flashcards

Cell Membranes & Transport- Unit 1.3 Flashcards

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1
Q

What are the functions of the plasma/cell membrane? (6)

A
  1. Is the boundary separating the living cell from its non-living surroundings.
  2. Controls which substances diffuse in and out of cell.
  3. Controls uptake of nutrients.
  4. Allows waste products to pass out.
  5. Responsible for secreting substances. (enzymes & glycoproteins)
  6. Cell recognition.
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2
Q

What is the main structure of the cell membrane?

A

Phospholipids that form a bilayer. (and proteins)

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3
Q

How are membrane proteins arranged?

A

Randomly

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4
Q

What are extrinsic proteins? (3)

A
  1. Proteins that occur on the surface of the bilayer/partly embedded in it. 2.PROVIDING STRUCTURAL SUPPORT.
  2. Many are receptor sites which bind with proteins like hormones and neurotransmitters.
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5
Q

What are intrinsic proteins? (3)

A
  1. Proteins that go right through the phospholipid bilayer.
  2. Some act as channels/carriers to facilitate diffusion of polar molecules across the membrane.
  3. Others can form pumps and carry out active transport against a concentration gradient.
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6
Q

What is the fluid mosaic model? (Singer and Nicholson 1972)

A

The phospholipids are fluid as each molecule can move in relation to the other within the membrane. The proteins form a mosaic pattern within the phospholipid bilayer.

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7
Q

What does cholesterol do?

A

Found in animal cells and fits between the phospholipid molecules, increasing rigidity and stability of the membrane.

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8
Q

What are glycolipids? (2)

A

(Lipids with a carbohydrate chain)
Found in outer layer of membrane.
Involved in cell to cell recognition.

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9
Q

What are glycoproteins? (1)

A

(Proteins with carbohydrate chain)

Stick out of some membranes.

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10
Q

What are the factors that affect cell permeability? (4)

A

Increasing:

  1. Temperature- cell membrane becomes unstable.
  2. Ethanol concentration- dissolve phospholipids.
  3. Sodium chloride concentration- reduces mobility of phospholipids.
  4. Detergent concentration- reduce surface tension of phospholipids.
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11
Q

What is diffusion?

A

The net movement of molecules from a high concentration to a low concentration until equilibrium is reached (equally distributed) down a concentration gradient.

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12
Q

What factors affect diffusion? (6)

A
  1. Concentration
  2. Diffusion pathway
  3. Surface area
  4. Thickness of membrane
  5. Increase in temperature
  6. Particle size
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13
Q

What is the difference between simple and facilitated diffusion?

A

Simple- diffusion of non-polar molecules across phospholipid bilayer.

Facilitated- Polar molecules using intrinsic proteins to facilitate transport across the membrane. Is limited by available intrinsic proteins.

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14
Q

What are channel proteins? (3)

A
  1. Consist of pores that are hydrophilic, allowing charged ions to pass through.
  2. Each protein is specific for one type of ion.
  3. Can open/close depending on need of cell.
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15
Q

What are carrier proteins? (3)

A
  1. Allow facilitated diffusion of larger polar molecules.
  2. Molecule attaches to protein at binding site and causes protein to change shape/rotate in membrane.
  3. This releases the molecule on the other side of the membrane.
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16
Q

What is active transport?

A

An ATP requiring process which ions & molecules move across membranes against a concentration gradient. (up)
Ions & molecules can move in opposite direction to diffusion.

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17
Q

What is a pump? How does it work?

A

An intrinsic protein that transports a molecule. (active transport)
ATP transfers phosphate group to pump on inside of membrane, causing the pump to change shape and transport molecules across the membrane.

18
Q

What are 2 processes involving active transport?

A

Protein synthesis & absorption of minerals.

19
Q

Why is diffusion not affected by respiratory inhibitors?

A

Does not require ATP (respiratory inhibitors stop ATP production)

20
Q

What is an example of a respiratory inhibitor that affects active transport?

A

Cyanide as it stops ATP production.

21
Q

What is osmosis?

A

The passage of water molecules from high water potential to lower water potential through a partially permeable membrane.

22
Q

What does 🔱cell mean?

A

Water potential of the cell

23
Q

What does 🔱s mean?

A

Solute potential

24
Q

What does 🔱p mean?

A

Pressure potential

25
Q

What is the equation used to describe the relationship between the forces in a plant cell?

A

🔱cell= 🔱s + 🔱p

26
Q

The more concentrated a solution…

more solutes dissolved

A

The more negative the water potential.

27
Q

At high concentrations of water…

A

The greater the potential energy.

water molecules free to move

28
Q

What is plasmolysis?

A

When water leaves a plant cell via osmosis, the cytoplasm & vacuole shrink, causing cell membrane to pull away from cell wall.

29
Q

What does a hypotonic external medium mean? (2)

A

Water potential of external solution is higher than solution inside cell.
Water will move in.

30
Q

What does a hypertonic external medium mean?

A

Has lower water potential outside than inside so water moves out of cell.

31
Q

What is an isotonic external medium? (2)

A

The same water potential inside and outside of the cell.

No net movement by osmosis.

32
Q

What happens to an animal cell when it’s external medium is hypotonic?

A

Cell swells and may lyse. (burst)

33
Q

What happens to a plant cell when it’s external medium is hypotonic?

A

Cytoplasm and vacuole swell and push against cell wall, becoming turgid.
Turgid plant cells support plant tissue and structures.

34
Q

What happens when an animal cell’s external medium is hypertonic?

A

The cell shrinks

35
Q

What happens when a plant cell’s external medium is hypertonic?

A

Cytoplasm & vacuole shrink causing cell membrane to pull away from cell wall. (plasmolysis)

36
Q

What happens when an animal cell’s external medium is isotonic?

A

It is optimal & normal

37
Q

What happens when a plant cell’s external medium is isotonic?

A

(also called incipient plasmolysis)

Cells become flaccid

38
Q

How do large particles enter cells?

A

Endocytosis.

39
Q

Name the 3 steps in endocytosis.

A
  1. Plasma membrane folds inwards.
  2. Continues to fold, engulfing material.
  3. Plasma membrane fuses to enclose material.
40
Q

What are the 2 types of endocytosis?

A

Phagocytosis (phagocytes engulfing microbes)

Pinocytosis (involves entry of liquid into the cell)

41
Q

What is exocytosis? (5)

A

Substances leaving the cell after being transported in transport vesicles (from RER)—>
through the cytoplasm—>
to the golgi body—>
and then to the cell membrane via secretory vesicles which fuse.
Contents are secreted outside the cell.

WJEC AS Biology (9 decks)

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