transport across membranes

What is an advantage of having a selectively permeable membrane?

Only certain substances are let in or out of cell.

diffusion

Diffusion is when molecules move from an area of high concentration to an area of low concentration.

example of diffusion in plants

• Carbon dioxide diffuses from the atmosphere and into the leaf through the stomata.

• Oxygen diffuses from the leaf into the atmosphere.

example of diffusion in humans

• Oxygen diffuses from the alveoli (lungs) into the capillary.

Name two processes that enter muscle cells from the blood by diffusion.

glucose and oxygen

Osmosis

movement of water molecules across a selectively permeable membrane from a region of high-water concentration to a region of low water concentration

How does osmosis differ from diffusion?

Diffusion does not require a selectively permeable membrane, but osmosis does

How does salting meat preserve it?

Salted meat causes the micro-organisms (Bacteria) on the meat to lose water and die due to osmosis

What do you think would happen to an animal cell in a less concentrated solution?

It would burst as it would gain water

State one location where osmosis occurs in humans:

Water moving from the large intestine into the blood

Turgor pressure

occurs when there is an outward pressure of the cytoplasm and vacuole against the cell wall of a plant

two features of a plant cell that allows it to remain turgid

Cell walls and a vacuole

What is the function of turgor pressure?

Provides strength for the plant

Why does the plant cell not burst?

cell wall

What happens to a cell when it loses turgor pressure?

The vacuole and cytoplasm shrivel, and the cell membrane moves away from the cell wall.

What happens to a plant when its cells lose turgor pressure?

wilting

How can plant cells return to a turgid condition?

• Place in distilled water

name the substance that causes the change in mass in plant tissue?

water

Role of osmosis in plant health

• roots absorb water from the soil

• causes turgidity, provides strength to the plant

What is active transport?

It is the movement of molecules against the gradient from an area of lower concentration to an area of higher concentration which requires energy.

What supplies energy to the cell to allow active transport to occur?

breakdown of ATP to ADP

Where does active transport occur in a plant?

root hairs absorb nutrients from soil

Why are there large numbers of mitochondria in cells where active transport occurs?

active transport requires energy

Passive transport

does not require energy for the movement of molecules

dependent variable in transport across membrane experiment

change in mass of the Visking tubing to determine the rate of osmosis.

control variable in transport across membrane experiment

same volume of solution adding to Visking tubing, same surface area of Visking tubing, same concentration of sucrose solution

procedure of transport across membrane experiment

• soak three strips of visking tubing in water to soften them

• partially fill each with same volume of sucrose solution w syringe

• pat each tube dry w tissue

• note fullness of each tube and record mass

• leave apparatus for 30 minutes to allow for osmosis

• remove bags, dry them and record fullness and mass

• make sure to set controls with distilled water