BIO MOD 1 IQ2

Diffusion: The movement of materials into and out of cells that takes place either passively or actively.

The movement of any molecules from a region of high concentration to low concentration of a substance until equilibrium is reached.

The rate of diffusion depends on the concentration gradient

higher difference between the concentration of substances, concentration gradient is steeper, diffusion will be faster - vice versa

→ speed up and slow down in terms of temperature, heat increases rate of diffusion.

Across a cell membrane: Particles pass between the phospholipid molecules from high to low concentration regions.

→ Carbon dioxide and oxygen easily move through the membrane via simple diffusion.

Facilitated diffusion: relatively large molecules (glucose and amino acids) and charged particles (sodium and chloride ions) do not readily pass through the phospholipid bilayer.

Require certain proteins: Carrier and channel proteins, assisting them diffusing them into the cell, known as facilitated diffusion.

KEY CONCEPTS:

Diffusion is the movement of particles from a region of high concentration to a region of low concentration until equilibrium is reached.

At equilibrium, there is no net movement of particles in either direction.

Diffusion does not require the input of energy.

Diffusion occurs faster with a higher temperature or a steeper concentration gradient.

Small, uncharged molecules such as oxygen and carbon dioxide will diffuse easily across the cell membrane.

Facilitated diffusion allows larger molecules and small electrically charged ions to diffuse across the cell membrane aided by carrier or channel proteins.

→ Passive movement: requires no energy input and includes the processes of osmosis and diffusion

→ Equilibrium: is reached when there is no net movement of molecules in either direction, moving equally in each direction. → no energy input required

→ Concentration gradient: movement from high concentration to low concentration, movement along a concentration gradient.

Osmosis (Special type of diffusion): The net movement of solvent molecules from a region of high solvent concentration to a region of low solvent concentration, through a semipermeable membrane.

When water is the solvent, just like diffusion the movement of water occurs along the concentration gradient and does not require an energy input.

Process: When water moves through the cell membrane, specific tiny protein channels in cell membrane ‘aquaporins’ (water pores).

→ The pressure created by water moving across a semipermeable membrane due to osmosis is called

the osmotic pressure.

The more water that moves across the membrane, higher osmotic pressure.

Isotonic: (iso = same)

Fluids inside and outside a cell are of equal solute concentration. → e.g. water molecules moving directions equally

Hypotonic: (hypo = lower)

Cells surrounded by a solution that contains a lower solute concentration. → water molecules into cells.

Hypertonic: (hyper = higher)

Cells surrounded by a solution of higher solute concentration → eg. water molecules out of cells.

Water: helps keep cells in shape, it forms a fluid that bathes tissues and also transports materials in solution.

Most common SOLVENT

→ Solution: formed when a solute (salt or sugar) dissolves in a solvent.

Concentrated solution: large amount of solute in relation to solvent, water in low concentration

Diluted solution: large amount of solvent in relation to solute, water in high concentration

→ Aquaporins (water pores): Special tiny hydrophilic pores in cell membranes

KEY CONCEPTS:

A solution is formed when a solute dissolves in solvent.

A concentrated solution has a high concentration of solute and a low concentration of water.

A dilute solution has a low concentration of solute and a high concentration of water.

Osmosis is the process by which water moves from a region of high concentration of water (dilute – low solute) to a region of low concentration of water (concentrated – high solute).

Osmosis requires no energy input.

The more water that moves across the membrane, the higher the osmotic pressure created.

Isotonic – fluids inside and outside a cell are of equal solute concentration – no net water

movement.

Hypertonic – a solution of higher solute concentration (lower water concentration) that

surrounds a cell – net movement of water molecules will be out of the cell.

Hypotonic – a solution of lower solute concentration (higher water concentration) that

surrounds a cell – net movement of water molecules will be into the cell.

ACTIVE TRANSPORT:

Active transport is the movement of molecules from a region of low concentration to a region of high concentration.

Active transport moves against the concentration gradient and requires the input of energy.

Example of phagocytosis:

A unicellular amoeba feeds on a smaller organism. The amoeba changes shape by sending out membrane

projections filled with cytoplasm that surround the prey, when membrane projections meat, membrane fusion occurs.

KEY CONCEPTS:

Endocytosis moves large molecules that cannot cross the cell membrane into a cell. It requires the expenditure of energy.

In endocytosis, the cell membrane changes shape and surrounds and engulfs the particle so that it enters the cell.

Phagocytosis is the process whereby solid particles are engulfed by the cell membrane.

Pinocytosis is the engulfing of fluid substances by the cell membrane.

Exocytosis involves a membrane-bound vesicle moving to the cell membrane, fusing with it and then releasing its contents to the exterior of the cell.

Surface area to volume ratio when exchanging materials across membranes: (surface area divided by volume)

SA: total area of the cell membrane around the cell

V: space taken up by the internal contents of the cell. → needs to have enough space to supply volumes and remove wastes.

→ A smaller cell has more surface area in relation to its volume – a higher SA:V. (long, flat cells)

Allows a faster movement of substances between the centre and the surface of the cell (in and out), quickly and easy removal of wastes.

→ A larger cell has a smaller amount of surface area in relation to its volume – a lower SA:V (eg. small spherical cells)

The efficiency of how a cell obtains its nutrients and removes its wastes is reduced as its size increases.

Reaches a point where diffusion is not fast enough to service the increasing volume of the cell.

Dividing to make two smaller more efficient cells

Concentration gradient when exchanging materials across membranes:

The concentration of the substance on either side of the membrane affects the rate of diffusion of that substance.

High concentration gradient: a large difference between the concentration on either side of the membrane, the substance will diffuse rapidly.

Low concentration: As concentration gradient decreases, rate of diffusion decreases and slows down.

Equilibrium: no net movement across the membrane.

→ Cytoplasmic streaming: within plants involves cytosol and organelles flowing around a cell in a circle movement.

Helps maintain a steeper concentration gradient, as cells diffuse they are rapidly moved to another area of the cell.

KEY CONCEPTS:

SA is calculated by finding the total area of the surface of the shape.