Unit B: Cells and Systems

Topic 4: Fluid Movement in Cells

Movement Through a Cell Membrane To be permeable means you let

everything go through, to be impermeable means you never let things through.

Cell membranes are selectively permeable. This means that they let some things through them (water particles), but control the movement of others (wastes and food particles).

Diffusion

Diffusion is how particles move. Particles move from an area of high concentration (there are lots of particles) to an area of low concentration (few of those particles are in that area).

An example of diffusion is how perfume particle spread throughout a room.

Why does diffusion happen?

It happens because particles bump into each. The more they bounce around, the more they spread out. This happens until they fill the area they are in.

Diffusion in Cells

If there are more particles of sugar outside of a cell than inside, than diffusion would cause the particles to spread into the cells (as long as the cell membrane allowed the particles in).

Osmosis

Osmosis is basically diffusion, but focussing strictly on water.

Water will move from an area of low concentration (pure water) to an area of high concentration (salt water) to balance the two sides out.

Osmosis in Cells

Water can freely move across cell membranes.

So if you eat salty foods, your cells will become highly concentrated with salt. Water will move from your bloodstream to your cells to balance things out. This triggers a reaction causing you to become thirsty.

Fluid Movement in Plants

Vascular tissue in plants connects roots to the leaves. It is involved in the transportation of water and sugar (food/energy).

There are two types of vascular tissue.

Phloem Tissue

Transports sugars created in the leaves through photosynthesis DOWN to the rest of the rest of the plant. These sugar particles move through diffusion.

Xylem Tissue

Transports water UP from the roots to the rest of the plant. This is done through osmosis of water from an area of lots of water (wet soil) to an area of less water (roots then vascular tissue and then plant cells)

Root hairs are made up of epidermal cells (the skin of the cell)

Photosynthesis

Occurs in specialized cells called palisade cells. These cells make up the green leaves of a plant.

They are designed flat and thin so they can soak up as much sunlight as possible.

They are full of chloroplasts.

Stomata

Cells in leaves that open up and allow gases to enter and leave the cell according to diffusion.

During photosynthesis plants take in as much carbon dioxide as possible. When they are changing their sugar into energy, they are take in as much oxygen as possible.

Stomata cells’ opening and closing are controlled by specialized ‘Guard Cells’.

Transpiration

Is the loss of water from a plant through evaporation, usually from the leaves.

Transpiration is not a problem as long as the supply of water is replenished by the roots. If no water comes into the plant, it dies.

Water Particles, Attraction, and Life

Water particles are attracted to each other. It is this attraction that allows water to pull itself up a plant through the xylem tissue.

This pushing (osmosis) and pulling (attraction) of water molecules is what has allowed life to occur on Earth.