Biology – Lecture 44

Cell Homeostasis and Transport

Cell Homeostasis

• Cells must maintain a constant internal environment and must be able to reproduce themselves when needed by the body.

Why do Cells Need Homeostasis?

• to function properly and stay alive• keeps the cell stable • help the organism function properly• the organism to remain healthy

How do cells maintain homeostasis?

• The waste is being transported away from the cell while it receives the nutrients it needs to continue to function.

What cell organelles help with cell homeostasis?

• Different parts of the cell work to constantly maintain homeostasis in the cell.

What main cell organelle helps with homeostasis?

The Main Homeostasis Organelle

• The cell membrane - the outer wall between the cell and the outside world.

• It protects the cell from outside stimuli that could disrupt a cell's homeostasis.

Cell Membrane’s Job

• Acts as the gatekeeper to what goes into and leaves the cell.

• It is made up of mostly fats (lipids) and protein and is selectively permeable, meaning it only lets certain molecules pass through the membrane

How does it decide what passes?

• When there is too much of a certain molecule inside the cell, the cell membrane allows some of the molecules to permeate the membrane and leave the cell.

What Else can pass?

• When there is too much of a molecule outside the cell and not enough inside the cell, the cell membrane will allow enough of the molecule to permeate inside to maintain homeostasis.

What cannot pass on its own?

• Charged molecules and large molecules cannot pass through the cell membrane, while small and uncharged molecules can.

Types of Cell Transport

• Passive Transport– Diffusion– Osmosis– Filtration– Facilitated Diffusion

• Active Transport

Passive Transport

• Passive forms of transport move molecules such as water and substrates across the cell membrane with no energy on the cell's part.

Diffusion

• Diffusion is the movement of material from an area of high concentration to an area with lower concentration.

The Concentration Gradient

• The difference of concentration between the two areas

• Diffusion will continue until this gradient has been eliminated.

Diffusion

• The movement of solutes down the concentration gradient.

• It moves the extra molecules from the area in which they have the highest concentration and spread them out.

How Does Diffusion Work?

• When there is too much of a certain molecule within the cell, the cell uses diffusion to transport some of those molecules into the environment.

• When there is not enough of a molecule within the cell, the cell uses diffusion to transport molecules from the environment into the cell.

Example of Diffusion

Osmosis

• The process of allowing water or other solvents to permeate the cell membrane.

• It is the diffusion of water molecules.

Example of Osmosis

Example of Osmosis

Hypertonic Solution

• No enough water in the cell• Too many molecules outside the cell• Causes the cell to shrink up

Isotonic Solution

• The right amount of water in the cell.• The right amount of molecules outside the

cell.• These are healthy cells.

Hypotonic Solution

• Too much water in the cell• Too much water outside the cell.• The cell swells and can burst open.

The Goal of Diffusion and Osmosis

• Maintain homeostasis in the cell by transporting molecules to create equilibrium between the inside of the cell and its environment.