Topic 2: 2.1

Question 1

Diffusion

Answer 1

Net movement of particles from an area of high concentration to low concentration, down a concentration gradient
- passive process -> no additional energy needed

Question 2

Effect of surface area to volume ratio

Answer 2

Larger organisms have a smaller surface area to volume ratio than small organisms
-> this means that gas exchange happens at a slower rate so large organisms have mass transport systems to keep up with the demand

Question 3

Gas exchange surfaces feautres

Answer 3

Gas exchange surfaces have features which increase the rate of diffusion
Examples:
- large surface area to volume ratio
- short diffusion distance
- steep concentration gradient
. Alveolar epithelium: gas exchange surface in mammals -> oxygen diffuses out of the alveoli into the blood and carbon dioxide diffuses into the alveoli from the blood

Question 4

Lung adaptations

Answer 4

. Lots of alveoli -> large surface area
. The alveoli and capillary endothelium are each one cell thick and their cells are flattened forming capillary and alveoli walls -> short diffusion pathway
. Good blood supply from capillaries and good ventilation with air -> steep concentration gradient

Question 5

Ficks law

Answer 5

Relates rate of diffusion to the concentration gradient, surface area and thickness of exchange surface
It states that:
. Surface area is directly proportional to the rate of diffusion
. Concentration gradient is directly proportional to the rate of diffusion
. Thickness of surface is inversely proportional to the rate of diffusion

Question 6

Membrane functions

Answer 6

Plasma membrane:
. Separates cell contents from surroundings
. Controls what comes in and out of cells
Membrane within cells:
. Separates contents of organelle from cytoplasm
. Controls passage of certain particles into and out of organelles
. Site of certain chemical reactions

Question 7

Membrane structure and properties: cholesterol

Answer 7

Type of lipid found in between phospholipids forming bonds with them
-> this makes the membrane more fluid at high temperatures and more rigid at low temperatures

Question 8

Membrane structure and properties: internal proteins

Answer 8

Embedded in plasma membrane for transport of particles
. Examples:
- channel proteins
- carrier proteins

Question 9

Membrane structure and properties: phospholipids

Answer 9

Form a continuos bilayer in membrane -> a single phospholipid is made up of a phosphate hydrophilic head and two hydrophobic fatty acid tails
. Formation of bilayer:
- the head is hydrophilic (attracts water) so the phosphate head flip outwards towards the tissue fluid or cytoplasm as both contain water
- the tail is made up of two fatty acids making it hydrophobic (repel water) so the fatty acid tails flip inwards

Question 10

Membrane structure and properties: external proteins

Answer 10

Receptors that carry out cell signalling on the surface of the membrane -> they bind to messengers (eg hormones) to create a change in that cell
. Examples:
-> glycoprotein -> made up of carbohydrates and protein
-> glycolipid -> made up of carbohydrate and fatty acid

Question 11

Fluid mosaic model

Answer 11

Shows that proteins are randomly distributed in cell membranes making them fluid
-> fluid: as phospholipids are free to move in the plane of the membrane
-> mosaic: proteins are embedded in various shapes, sizes and positions

Question 12

Ósmosis

Answer 12

Movement of water molecules from an area of low concentration of solutes (high water concentration)to and area of high concentration of solutes (low water concentration) though a partially permeable membrane
. Free water molecules. Those that are not used as solvent

Question 13

Permeability of membranes

Answer 13

Membranes are partially permeable which means that they allow the transport of certain particles -> all membranes will be completely permeable to small uncharged particles which pass in between the phospholipids
-> charged particles: they’re water-soluble substances so they’re repelled by the phospholipid tail and so can’t go through membrane
-> large particles: they don’t fit the gaps between phospholipids and so can’t go through membrane

Question 14

Effect of temperature un membrane permeability

Answer 14

. At high temperatures the phospholipids can move around more because they have more energy and so aren’t as closely packed together and increases permeability
-> at extremely high temperatures the proteins in the membrane denature and water expands in the cell causing pressure on the membrane which deforms the cell membrane structure and so it looses control over what enters
. At low temperatures the phospholipids can’t move around because they don’t have much energy and so they are closely packed together and this decreases permeability

Question 15

Facilitated diffusion

Answer 15

Diffusion of particles in cell membrane down a concentration gradient through carrier and channel proteins
-> passive process

Question 16

Carrier proteins

Answer 16

Move large molecules down their concentration gradient
-> each carrier protein is specific to one particle only
1. A large molecule attaches to a carrier protein in the membrane
2. The particles kinetic energy cause the protein shape releasing the molecule on the other side of the membrane

Question 17

Channel proteins

Answer 17

Form pores/ channels in in the phospholipid in the membrane for charged particles to diffuse through down their concentration gradient preventing them from being repelled by the fatty acid tails
-> each channel protein is specific to one particles only

Question 18

Active transport

Answer 18

Movement of particles against a concentration gradient through carrier proteins using ATP
. ATP: produced by respiration -> its hydrolysed in the cel to release energy
-> used as an immediate source of energy in the cell

Question 19

Endocytosis

Answer 19

Bulk transport of large molecules into the cell using energy from ATP
1. Cell membranes surrounds the molecule
2. Membrane pinches off to form a vesicle inside the cell containing the molecule

Question 20

Exocytosis

Answer 20

Bulk transport of large molecules out of the cell using energy ATP
1. Vesicle containing the molecule pinch off from the sacs of the Golgi apparatus and moves towards the cell membrane
2. Vesicles fuses with the cell membrane and it:
- releases the molecule out of the cell
- inserts the molecule into the cell membrane

Question 21

What evidence led to the fluid mosaic model

Answer 21

1. Microscope images show proteins in the bilayer
2. Phospholipids form a bilayer
3. Lipid-soluble molecules move faster across membranes
4. Coloured/tagged/labelled proteins can be seen to move within a membrane