▪️C1.3 -cell Memebranes and transport

Question 1

Why are phospholipids a important component of the cell surface membrane?

Answer 1

• they can form bilayers
• inner layer of phospholipids has its hydrophilic head pointing in towards the cell, interacting with the water in cytoplasm
• outer layer has its hydrophilic head pointing outwards, interacting with the water surrounding the cell
• hydrophobic tails point towards each other, to the centre membrane
• phospholipid component of a membrane allows lipid soluble molecules across but not water soluble molecules

Question 2

Where are proteins in a cell membrane?

Name the 2 forms of protein present

Answer 2

Scattered throughout the phospholipid Bilayer of the membrane embedded as either extrinsic or intrinsic proteins

Question 3

Describe extrinsic proteins and their purpose

Answer 3

On the surface of the bilayer.
Provide structural support
Form recognition sites by identifying cells and receptor sites for hormone attachment

Question 4

Describe intrinsic proteins and their purpose

Answer 4

Extended across both layers of the phospholipid bilayer

Includes carrier and channel proteins

Question 5

What do carrier proteins (intrinsic proteins) do?

Answer 5

They transport water soluble substances across the cell membranes

Question 6

What do channel proteins (intrinsic proteins) do?

Answer 6

Allow active transport of ions across the membrane through forming channels

Question 7

Why is the fluid mosaic structure called the fluid mosaic structure?

Answer 7

• the individual phospholipid molecules can move within a layer relative to one another (fluid)
• the proteins embedded into the bilayer vary shape and size and pattern (mosaic) lol

Question 8

Where in the cell membrane is cholesterol found? What is it’s purpose?

Answer 8

In the membranes of animal cells, between the phospholipid molecules, making the membrane more rigid and stable

Question 9

Where in the cell membrane are glycoproteins and glycolipids found?

Answer 9

In the outer layer of the membrane.

Question 10

What is the outer layer around the cell membrane called? What is it’s role?

Answer 10

The glycocalyx

The molecules in the glycocalyx have roles as hormone receptors or in cell-to-cell recognition

Question 11

What can diffuse across the membrane?

Answer 11

Lipid soluble substances such as vitamin A, small molecules like oxygen and carbon dioxide can dissolve in the phospholipid and diffuse across the membrane

Question 12

How does the phospholipid layer being hydrophobic effect diffusion is different molecules

Answer 12

Lipid soluble molecules move through the cell membrane more easily than water soluble substances

Question 13

Name molecules that struggle to diffuse through membrane

Why is this?

Answer 13

Glucose, polar molecules and jk s can’t readily diffuse through the phospholipids
This is because they are water soluble

Question 14

How do water soluble substances pass through the cell membrane?

Answer 14

They pass through intrinsic protein molecules which form water filled channels across the membrane

Question 15

What is the name for a membrane that picks what to diffuse in and out

Answer 15

Selectively permeable membrane

Question 16

Define simple diffusion

Answer 16

The movement of molecules or ions from a region of high concentration to lower concentration down a concentration gradient until equilibrium is reached. It is a passive process it does not require atp

Question 17

Name the factors affecting simple diffusion:

Answer 17

• the concentration gradient (greater difference the more molecules diffuse in a given time)
• thickness of the exchange surface/distance of travel where diffusion takes place (thinner=more molecules diffuse)
• the surface area is the membrane
• size of diffusing molecules (smaller diffuses faster)
• temperature
• nature of diffusing molecules (fats diffuse faster than water soluble molecules)

Question 18

Name the rate of diffusion equation:

Answer 18

(Surface area x difference in concentration) divided by the length of diffusion pathway

Question 19

Define facilitated diffusion.

Answer 19

The passive transfer of molecules or ions die. A concentration gradient, across a membrane by protein carrier molecules In the membrane

Question 20

Where does facilitated diffusion occur?

Answer 20

At a specific sit on the plasma membrane wher there are transport protein molecules (intrinsic carrier/channel proteins)

Question 21

Define channel proteins in detail

Answer 21

Molecules with pores lines with polar groups. As the channels are hydrophilic, water soluble ions can pass through. The channels open and close according to the needs of the cell

Question 22

Define carrier proteins in detail

Answer 22

Allow diffusion of larger polar molecules such as sugar and amino acids across the membrane. A molecule attaches to its binding site, on the carrier protein. The carrier protein changes shape and released the molecule on the other side of the membrane

Question 23

Describe how larger molecules e.g amino acids diffuse through a cell membrane

Answer 23

A molecule attaches to the binding site, on the carrier protein. The carrier protein changes shape and releases the molecule on the other side of the membrane

Question 24

Does the use of carrier proteins use ATP

Answer 24

No, carrier and channel proteins increase the rate of diffusion down a concentration gradient without energy in the form of ATP

Question 25

Define active transport

Answer 25

A process in which ions and molecules move from an area of low concentration to high concentration against a concentration gradient through a semi permeable membrane, it is an active process it requires ATP

Question 26

Name some features of active transport

Answer 26

1- ions/molecules are moved from a lower to higher concentration against a concentration gradient 2- requires energy in the form ATP. Anything that affects respiration will effect active transport 3- process occurs through intrinsic carrier proteins spanning the membrane 4-rate is limited by the number and availability of carrier proteins

Question 27

Name some processes involving active transport

Answer 27

Muscle contraction, nerve impulse transmission, reabsorption of glucose in the kidney nephron and mineral uptake into plant root hair cells

Question 28

Describe the process of ATP

Answer 28

1) Molecule or ion combines with a specific carrier protein on the outside of the membrane 2) ATP transfers a phosphate group to the Carrie protein on the inside of the membrane 3) carrier protein changes shape and carried the molecule across the membrane, to the inside of the cell 4) molecule is realised into cytoplasm 5) phosphate ion is released from the carrier molecule back to the cytoplasm and recombined with ADP to form ATP 6) carrier protein returns to its original shape

Question 29

What happens when an active transport graph Levels off?

Answer 29

The carrier proteins are saturated

Question 30

Name something that can stop active transport | Why?

Answer 30

A respiratory inhibitor such as cyanide can stop active transport This is because they prevent aerobic respiration and the production of ATP in the mitochondria

Question 31

Define co-transport

Answer 31

A type of facilitated diffusion that brings molecules and ions into cells together on the same transport protein molecule

Question 32

Name an example of co-transport

Answer 32

Sodium-glucose co-transport is significant In absorbing glucose and sodium ions across cell membranes and into the blood in the kidney nephron

Question 33

Describe how co-transport occurs

Answer 33

1- a glucose molecule and two sodium ions outside the cell attach to a carrier protein In the cell membrane 2- the carrier protein changes shape and deposits the glucose molecule and the sodium ions inside the cell 3-the glucose molecule and sodium ion separately diffuse through the cell to the opposite membrane

Question 34

What is the water potential of pure water

Answer 34

0

Question 35

What happens to the value of water potential when you add a solute

Answer 35

Addition of solute to pure water lowers the water potential making it a negative value

Question 36

Define osmosis

Answer 36

The net movement of water molecules from an area of High water potential to low water potential down a concentration gradient through a semi permeable membrane, it is a passive process it does not require ATP

Question 37

Define water potential

Answer 37

The tendency for water to move into a system, from an area of higher water potential to lower water potential. Water potential is decreased by the addition of a solute. Pure water has a water potential of 0

Question 38

What does solute potential measure?

Answer 38

Measures how easily water molecules move out of a solution

Question 39

Define turgid

Answer 39

A plant cell that holds as much water as possible, preventing further entry of water as the cell can’t expand further

Question 40

Name the 2 opposing forces in a plant cell

Answer 40

1) solute potential, due to diluted in the vacuole and cytoplasm, pulls water in to the cell meaning water is less likely to move out 2) pressure potential, a force which increases chance of water moving out

Question 41

Name the osmosis pressure equation

Answer 41

Water potential of cell= pressure potential + solute potential

Question 42

Describe when a hypotonic situation occurs

Answer 42

If the water potential of the external solution is less negative (greater) than the solution inside the cell. Water would flow into the cell

Question 43

Describe when a hypertonic situation occurs

Answer 43

If the water potential of the external solution is more negative (less) than the solution inside the cell Water flows out of the cell

Question 44

Describe how a isotonic situation occurs

Answer 44

If the cell has the same water potential as the external solution No net water movement

Question 45

Define the process of plasmolysis | What happens when complete?

Answer 45

Occurs when plants in s hypertonic solution lose water by osmosis and the vacuole shrinks and cytoplasm draws away from cell wall When complete the cell is flaccid and plant wilts

Question 46

Define the process of incipient plasmolysis

Answer 46

Occurs when the external concentration is High enough so just enough water is lost do the membrane begins to pull away from the cell wall

Question 47

What is the pressure potential of a cell in incipient plasmolysis? Why?

Answer 47

0 | Because the cell wall does not exert any pressure on the cytoplasm

Question 48

What is the pressure equation of a cell in incipient plasmolysis

Answer 48

Water potential =solute potential

Question 49

What is the value of water potential in a fully turgid cell?

Answer 49

0

Question 50

What is the pressure equation in a fully turgid cell?

Answer 50

Pressure potential = - solute potential

Question 51

Why is turgor important to plants

Answer 51

Provides support, maintains their shape and holds them upright

Question 52

Name the water potential equation in an animal cell

Answer 52

Water potential = solute potential

Question 53

Describe the process of haemolysis

Answer 53

If red blood cells are in distilled water, water enters by osmosis and they burst as they don’t have a cell wall

Question 54

Describe the process of crenation

Answer 54

When red blood cells are placed in concentrated salt solution, water leaves the cells and they shrink

Question 55

Name the 2 methods of bulk transport

Answer 55

Endocytosis | Exocytosis

Question 56

When does endocytosis occur?

Answer 56

When material is engulfed by extensions of the plasma membrane and cytoplasm, forming a vesicles

Question 57

Name the 2 types of endocytosis

Answer 57

Phagocytosis | Pinocytosis

Question 58

Define phagocytosis

Answer 58

The Uptake of solid material that is too large to be taken in by diffusion or active transport

Question 59

Describe the process of phagocytosis

Answer 59

When granulocytes engulf Bactria, a lysosomes fuses with the vesicle formed and enzymes digest the cells, products are absorbed into cytoplasm

Question 60

Define exocytosis

Answer 60

Process where substances leave the cell, having been transported trough the cytoplasm in a vesicle, which fuses with the cell membrane.

Question 61

Give an example of something that is secreted by exocytosis

Answer 61

Digestive enzymes

Question 62

Why is endocytosis and exocytosis active processes

Answer 62

The cell membrane has to change shape which requires energy is the form of ATP, generated by the cells respiration

Question 63

Why is the cell membrane being fluid vital to the cell?

Answer 63

Because the cell membrane flows with endocytosis decreasing the overall are of the cell membrane and exocytosis increasing it

Question 64

Suggest two reasons why transport across the membrane is vital to the cell

Answer 64

- Maintains water potential in cells - obtain oxygen/remove CO2 - obtain minerals/nutrients e.g glucose

Question 65

Describe the role of the cell wall in generating pressure potential

Answer 65

Cell wall is inelatic/won’t stretch Water passes into the cell via osmosis and the protoplast swells/expands This pushes against cell wall and due to its resistance generate a pressure potential

Question 66

Suggest 2 functions of membrane proteins

Answer 66

1. Acts as recognition sites for cell-to-cell recognition of individual cells 2. transport proteins allow water soluble/ polar substances to penetrate the membrane

Question 67

How does oxygen enter the cell

Answer 67

-by simple diffusion, through the phospholipid bilayer

Question 68

Describe how phosphate ions enter the cell

Answer 68

Phosphate ions travel by facilitated diffusion/active transport through carrier proteins

Question 69

Describe how the solubility in lipid affects the rate of diffusion through a membrane

Answer 69

As lipid solubility increases, the rate of diffusion increases as membrane contains double layer of phospholipids :: lipids can diffuse through the membrane more easily

Question 70

Describe how molecular size affects the rate of diffusion

Answer 70

The larger the molecule the slower the rate of diffusion as they are more difficult to pass between phospholipid molecules