Biology T1 - Movement of substances into and out of cells

What special feature does the cell surface membrane have?

It is selectively permeable

What is a selectively permeable membrane?

A membrane that allows certain molecules or ions to pass through

What are the 3 ways materials may pass in and out of a cell?

1. Diffusion

2. Osmosis

3. Active transport

What is the definition of a concentration gradient?

When there is a region of high concentration leading to a region of low concentration.

Process of a concentration gradient

→Molecules and ions in a liquid or a gas show random movement due to their kinetic energy.
→Particles collide more often when they are close (concentrated) together.
→They tend to diffuse or spread out until they are spaced evenly throughout the gas or liquid.
→The difference in the concentration is called as concentration gradient.
→Molecules and ions can move from one place to another, but only until an equilibrium has been reached.
→If no concentration gradient exists between two places, it hinders the absorption of useful particles.

What is the definition of diffusion?

The net movement of particles (molecules/ions) within a gas or liquid from a region of high concentration to a region of lower concentration, down a concentration gradient. This process occurs until an equilibrium is reached.

What are the qualities of diffusion?

→Cells do not need to expend any energy for diffusion to take place
→Is a passive process
→Takes place through semi permeable membranes depending on the size of the molecule

What are some examples of diffusion?

→Gas exchange at the alveoli- O2 diffuses from air to blood, CO2 diffuses from blood to air.
→Gas exchange for respiration- O2 diffuses from blood to cells, CO2 diffuses in the opposite direction.
→Products of digestion dissolve in with water and diffuse across the walls of small intestine.
→Gas exchange from photosynthesis- CO2 diffuses from air to leaf, O2 diffuses from leaf to air.
→Diffusion can also take place through semi permeable membranes. This depends on the size of the molecule.

What factors affect the rate of diffusion?

1. Concentration gradient

2. Diffusion distance

3. Surface area to volume ratio

4. Temperature

How does concentration gradient affect the rate of diffusion?

→The greater the difference in concentration between both areas, the faster the rate of diffusion

How does diffusion distance affect the rate of diffusion?

→The shorter the distance molecules have to travel, the faster the rate of diffusion.

How does surface area to volume ratio affect the rate of diffusion?

→The larger the surface area to volume ratio, the faster the rate of diffusion, as more molecules can pass through the surface simultaneously.

What experiment is done to investigate the effect of S.A:Volume on the rate of diffusion

→3 cubes of agar are prepared containing the indicator, phenolphthalein
→Placed in hydrochloric acid which diffuses into cubes
→As it diffuses, it will turn the indicator colorless
→The larger the cube is, the smaller the surface area : volume ratio, the slower the rate of diffusion

How does temperature affect the rate of diffusion?

→The higher the temperature, the faster the rate of diffusion.

What is osmosis?

→The net movement of water molecules from a region of high water potential to a region of low water potential, down a water potential gradient, through a partially permeable membrane

Qualities of osmosis

→The biochemical processes in living cells always take place in an aqueous medium.
→Living cells are separated from their surroundings by the partially permeable cell surface membrane.
→Osmosis is a passive process. It does not require energy.
→The factors that affect diffusion affect osmosis as well.

Examples of osmosis

→Absorption of water by plant roots
→Re-absorption of water at kidney tubules
→Re-absorption of water by the alimentary canal

Which solutions have specific amounts of water molecules?

→A dilute solution has many water molecules (high water potential)
→A concentrated solution has less water molecules in comparison to soluble particles (low water potential)

Diagram of osmosis process

What happens to an animal cell in a concentrated solution?

1. Outside is highly concentrated (more soluble)

2. Inside is low concentrated/more dilute/more water

3. High water potential inside

4. Water moves OUT

5. Cell shrinks

What happens to an animal cell in a dilute solution?

1. Outside is low concentrated (less solute)

2. Inside is highly concentrated/less dilute/less water potential inside

3. Water moves IN

4. Cell swells

5. When too much water enters a red blood cell, because the red blood cell does not have a cell wall, the cell will burst.

What is hypertonic?

When theres a lot of water on the outside

What is hypotonic?

When there are low levels of water on the outside

What is isotonic?

Equal levels of water on the inside and outside

What happens to an animal cell in a solution which has the same water potential as it’s cytoplasm?

1. Equal concentration outside and inside

2. Equal water potential outside and inside

3. Water moves IN and OUT at the same rate - no net same rate - as net movement of water

4. Cell stays the same

What does turgid mean?

Cells are described as turgid when they are swollen due to a high-water content.

What does turgor pressure mean?

The pressure on the cell wall from the cell membrane pushing upon it. This is a result of the cell becoming turgid as water moves into the cell via osmosis.

What does flaccid mean?

Occurs when water moves out of the cell via osmosis. The cell shrinks but the cell membrane does not peel away from the cell wall. If more water leaves the cell, it becomes plasmolysed.

What are plasmolysis?

Occurs when there is too little water in cells after water moves out by osmosis. In plant cells, the cell membrane peels away from the cell wall

What happens when an animal cell is placed in a diluted solution?

1. When a plant cell is placed in a diluted solution, water moves into the cell as the pressure inside the cell increases (turgor pressure) the cell becomes turgid

What happens when an animal cell is placed in a concentrated solution?

1. When a plant cell is placed in a concentrated solution, water will leave the cell by osmosis. This cell will lose mass and become flaccid

2. If the cell is not moved out of the solution, water will continue to leave the cell and the cell membrane will detach from the cell wall and becomes plasmolysis.

What is active transport?

Movement of molecules or ions from a region of low concentration to a region of high concentration (against the concentration gradient) using energy from cellular respiration.

What does active transport use to embed within the cell membrane?

Active transport uses protein channels that are embedded within the cell membrane

What are examples of active transport?

→Uptake of minerals from soil by root hair cells
→Uptake of glucose by epithelial cells of the villi
→Glucose is actively transported back into the blood from the glomerular filtrate in the kidneys