National 5 Biology | Unit 1 | Key Area 2: Transport Across Cell Membranes

Why treat the cell membrane in high temperatures?

The extreme heat ==denatures the proteins== present in the cell membrane.

Give examples of internal cell structures surrounded by a cell membrane:

Nucleus, mitochondria, sap vacuole, chloroplast

What is the function of the cell membrane?

-Controls what enters and exits the cell (selectively permeable)
-Allows different sets of conditions to be maintained in different 'compartments'.

Why treat the cell membrane with acid?

The acid pH conditions ==denature the proteins and the overall shape==.

Why treat the cell membrane with alcohol?

The alcohol ==dissolves the (phospho)lipids== present in the cell membrane.

The cell membrane consists of _____ and _____ molecules.

Protein; phospholipid

What is a phospholipid?

A molecule made from phosphorus (phospho-) and fat (-lipid)

Diffusion

The process by which ==molecules move from an area of higher concentration to an area of lower concentration== until the concentration becomes equal.

Concentration gradient

The ==difference in concentration== that exists between an area of higher concentration and an area of lower concentration.

During diffusion, the movement of molecules always occurs _____ a concentration gradient from _____ to _____ concentration.

Down; higher; lower

All solids, liquids and gases are made of _____. In liquids and gases, these can move around _____. In solids, they are _____ free to move.

Molecules; freely; less

Diffusion requires a _____ _____ of the substance.

Concentration gradient

Diffusible substances are _____, _____ and _____ solids.

Gases; liquids; dissolved

During diffusion, there must not be any form of _____ between the regions of differing concentration.

Barrier

Diffusion is a _____ process and will occur in _____ or _____ systems.

Passive; living; dead

Factors to increase the rate of diffusion include:

-Increasing the temperature
-Increasing the concentration gradient
-Increasing the surface area

Diffusion is used by cells for the entry of useful substances such as _____ and _____, as well as for the removal of _____ substances such as carbon dioxide.

Oxygen; glucose; waste

Movement of materials between cells in multicellular organisms is normally carried out by _____ _____ _____, eg. the bloodstream.

Special transport systems

As cells become _____, diffusion cannot occur fast enough to transport all the materials required. This is because the _____ _____ becomes relatively small compared to the overall _____.

Larger; surface area; volume

Larger objects have _____ surface area:volume ratios than smaller objects. Therefore a cell cannot become too large, otherwise its _____ _____ would be too small for adequate _____ of molecules in and out.

Smaller; surface area; transport

The cell membrane contains tiny _____ through which molecules can diffuse. The molecules have to be _____ than these in order for them to pass through the cell membrane.

Pores; smaller

The cell membrane is _____ to _____ molecules such as protein and _____ substances such as starch.

Impermeable; large; insoluble

The cell membrane is _____ permeable to _____ molecules such as oxygen, glucose, water and carbon dioxide.

Fully; small

The cell wall (of plant cells) have very large _____, which means it is _____ permeable to dissolved substances, regardless of size.

Pores; fully

Osmosis

The movement of ==water molecules== from an ==area of higher water concentration to an area of lower water concentration== ==through a selectively permeable membrane==.

During osmosis, the movement of molecules always occurs _____ a concentration gradient from _____ to _____ concentration.

Down; higher; lower

For water to enter a cell via osmosis, it must be _____.

Alive

If water enters a cell via osmosis, it means the water concentration outside of the cell is _____ than the water concentration inside the cell. The water molecules move along the _____ _____.

Greater; concentration gradient

If water exits a cell via osmosis, it means that the water concentration outside the cell is _____ than the water concentration inside the cell. The water molecules move to _____ the concentration in both areas.

Lower; equalise/neutralise

If there is no overall movement of water in the cell and its surroundings, then the concentration gradient is _____ in both areas.

Even

Even if the concentration gradient is even, molecules will still _____ to move.

Continue

If an animal cell is placed in a concentrated salt solution, what would happen?

==Water would leave the cell==, since there is a lower water concentration outside of the cell than inside. Since there is no cell wall to retain the shape, ==the whole cell would shrink==.

If a plant cell was placed in a concentrated salt solution, what would happen?

==Water would diffuse out the cell by osmosis==, since there is a lower water concentration outside of the cell than inside. Most of the water lost comes from the vacuole and cytoplasm, so the ==contents of the cell shrinks==, but the ==cell wall retains its shape==.

Plasmolysis

This happens when ==a cell shrinks inside its cell wall due to extreme water loss==, while the cell wall itself remains intact. This is a ==reversible change== (pure water).

If an animal cell was placed in pure water, what would happen?

==Water would pass into the cell==, since there is a higher water concentration outside the cell than inside. Since there is no cell wall, ==the cell would eventually burst==.

If a plant cell was placed in pure water, what would happen?

==Water would diffuse into the cell by osmosis==, since there is a higher water concentration outside the cell wall than inside. The ==cell wall prevents the cell from taking in too much water== and bursting.

When no more water can enter a cell via osmosis, the cell is said to be _____

Turgid

Turgor is very important to plants, as turgid cells provide _____ for the stem. If a non-woody plant loses too much water it will _____.

Support; wilt

Water will constantly enter an amoeba via _____. The unicellular animal uses a _____ ____ to constantly remove water. It is an energy-required process, since water is moved _____ its concentration gradient.

Osmosis; contractile vacuole; against

Active transport requires _____ from the cell's _____.

Energy; metabolism

Active transport uses _____ in the cell membrane to transport substances across the membrane.

Proteins

Active transport moves molecules _____ the concentration gradient. Molecules are moved from an area of _____ concentration to an area of _____ concentration.

Against; lower; higher

During active transport, an _____ concentration of molecules or ions can be maintained on one side of the membrane.

Uneven

What are the benefits of active transport?

-Useful molecules can be kept inside a cell (eg. glucose)
-Unwanted molecules can be kept outside of a cell (eg. carbon dioxide)