Chapter 8

Question 1

what is the plasma membrane

Answer 1

The outer boundary of the cell that separates if from other cells and the external environment. Determines which substances get into or out of a cell

Question 2

what does selectively permeable mean

Answer 2

allows some substances but not others to pass across it

Question 3

what is the structure of cell membranes

Answer 3

is a fluid mosaic model composed of phospholipid molecules which are arranged in two layers, know as a bilayer. Each phospholipid molecule has a head that is hydrophilic and a tail that is hydrophobic. Arranged with heads on the outside and tails on the inside. Embedded in the bilayer of the membrane are cholesterol and protein molecules. Many of these proteins are involved in the movement of substances from one side of the membrane to another. DRAW DIAGRAM

Question 4

Define Hydrophilic

Answer 4

water loving

Question 5

Define Hydrophobic

Answer 5

Water hating

Question 6

what are adhesion proteins

Answer 6

membrane proteins that help link cells together

Question 7

what are transport proteins

Answer 7

protein that carriers molecules across membranes

Question 8

what are receptor proteins

Answer 8

protein that binds hormones and other signal molecules

Question 9

what are recognition proteins

Answer 9

Identifies the cell as ‘self’ to prevent attack by the body’s immune system

Question 10

What is an example of transport proteins allowing specific substances to move across the membrane

Answer 10

Rapid movement of ions when a nerve is stimulated. Causes a dramatic change in the differences in positive and negative charges across the membrane and explains how the electrical charge of a nerve impulse is transmitted along nerve cells

Question 11

what is a passive process

Answer 11

When the cells energy, which comes from respiration, is not required

Question 12

What is an active process

Answer 12

Process that require the cells energy for the transfer to occur

Question 13

what is diffusion

Answer 13

• The spreading out of particles so that they are eventually distributed over the space available.
• Occurs in gases and liquids because the molecules of gases and liquids are constantly moving.
• They move in random directions and in straight line until they hit an obstacle.
• Molecules moving away from an area in which they are concentrated won’t collide as much as those moving towards the high concentration.
• Therefore stay on straight paths for longer, evenly spreading over the space available

Question 14

what is the difference between diffusion and concentration gradient

Answer 14

Diffusion is the net movement of particles from a region of high concentration to low concentration. The difference in the particle concentration between the two regions is the concentration gradient

Question 15

Why does a sugar cube dissolve in a beaker of water

Answer 15

When the sugar cube is first placed into the water, there is a lower concentration of water in the sugar cube and higher concentration of water else where in the beaker. Therefore there is a diffusion gradient for the water but is in opposite direction to that for the sugar.

Question 16

what are the two types of diffusion and what substances undergo them

Answer 16

• Diffusion (O2, H2O, CO2 and other small uncharged particles)
• Facilitated Diffusion (charged particles like sodium and large molecules like glucose)

Question 17

what is facilitated diffusion

Answer 17

a form of diffusion that requires the substance to be attached to a specific carrier molecule to move across the membrane

Question 18

what is the difference between carrier and channel

proteins in facilitated diffusion

Answer 18

• Carrier proteins bind to specific molecules on one side of the membrane, change shape and release the substance on the other side
• Channel proteins form narrow passageways through which small ions can diffuse rapidly from a high to low concentration. only ions of specific size and shape can pass through a channel protein

Question 19

Explain the role of cholesterol in a plasma membrane

Answer 19

in animal cells, cholesterol interferes with interactions between the lipid tails, making the membrane more flexible. In plant cells, it is phytosterol (not cholesterol)

Question 20

what is a solvent

Answer 20

a substance in which another substance can be dissolved to create a solution (eg water)

Question 21

what is a solute

Answer 21

a substance that can be dissolved in another substance (eg salt)

Question 22

what is osmosis

Answer 22

the diffusion of water across a semipermeable membrane from an area of high water concentration (low solute) to an area of low water concentration (high solute)

Question 23

define hypertonic

Answer 23

a solution with higher solute concentration compared with another solution (Hyper = ‘higher’)

Question 24

define hypotonic

Answer 24

a solution with lower solute concentration compared with another solution (Hypo = ‘lower’)

Question 25

define isotonic

Answer 25

describes fluid with equal solute concentration to another fluid (iso = ‘same’)

Question 26

why must red blood cells remain in an isotonic solution?

Answer 26

if the plasma surrounding blood cells becomes hypertonic, water will move out of the cells by osmosis and will shrink and become crinkled. if the blood plasma is diluted by water, the blood cells will swell and burst

Question 27

what happens to plant cells in a hypotonic solution

Answer 27

when a hypotonic solution surrounds a plant cell, water molecules diffuse into cytoplasm and then into vacuole. The vacuole swells, pushing the cytoplasm and plasma membrane against the cell wall. The tough cell wall prevents the cell from bursting.

Question 28

what is endocytosis

Answer 28

the movement of solids or liquids into a cell from the environment via vesicle formation

Question 29

what is exocytosis

Answer 29

the movement of solids or liquids from a cell to the environment via vesicle formation

Question 30

what is pinocytosis

Answer 30

Taking liquids into the cell during endocytosis

Question 31

what is phagocytosis

Answer 31

Taking solids into the cell during endocytosis

Question 32

what are the physical factors that effect transport, give examples

Answer 32

size and shape. small molecules like water, oxygen and carbon dioxide are able to slip between the phospholipids

Question 33

what are the chemical factors that effect transport, give examples

Answer 33

Charged ions such as Na+, K+ and Ca+ which are hydrophilic cannot cross gthe hydrophobic interior of the membrane

Question 34

why are cells so small

Answer 34

As a cell grows, its ability to exchange enough materials to support its increasing volume is diminished because the volume increases at a greater rate than the surface area. A large cell could not support itself because it would not have enough surface area to absorb the nutrients required and remove wastes produced