Movement of Substances

The cell membrane of a cell is a ________ _________ membrane

Partially permeable

What are the two important things a cell membrane does

• acts as a boundary between the cell contents and its surroundings (separates interior from exterior)

• controls what enters and sits cell

What is the cytoplasm

The place where all the cell’s chemical reactions take place

What are the things a cell needs

• raw material for growth

• food for energy

• oxygen for respiration

What things does a cell need to remove

Waste products such as CO2

What are the three ways substances may move in and out of cells

• Diffusion

• Osmosis

• Active transport

What is diffusion

The passive (does not require energy) of particles from a region of high concentration to a region of low concentration down a concentration gradient until equilibrium is reached

What does passive mean in this context

Does not require energy

What is a concentration gradient

Difference in concentration of a substance between two areas

Since diffusion may take some time until equilibrium is reached, what has happened

living organisms have developed certain adaptations to speed up diffusion

What are these adaptations

• Distances over which diffusion take place are short: the shorter the distance the faster the rate of diffusion

• Concentration gradient is maintained: higher the concentration gradient, the faster the rate of diffusion

• Surfaces over which diffusion take place are large: the larger the surface area the faster the rate of diffusion

• Particle size is small: the smaller the particle size, the faster the rate of diffusion

• Diffusion happens when temperatures are high: the higher the temperature, the greater the kinetic energy of the particles, thus the greater number of collisions between particles

Summary of last flash card

• Shorter distances

• Higher concentration gradients

• Larger surface areas

• Small particle sizes

• High temperatures

D - Distance

C - Concentration gradient

SA - Surface area

P - Particle

T - Temperature

Dreamy clouds sail past trees

Osmosis is the diffusion of

Water molecules

Since water is vital for all living organisms is must be

Transported around living organisms

Since we cannot speak of water as being concentrated, we use the phrase

Water potential

Definition of Osmosis

The passive (does not require energy) of water molecules from a dilute to a more concentrated solution, though a selectively permeable membrane

What is the main difference in structure between an animal cell and a plant cell

The presence of a tough and elastic cell wall in plant cells, and the absence of it in animal cells

Because of these different structures does osmosis have a different effect on animal cells and plant cells

Yes

Explain: Hypertonic Solution

- Hypertonic solution: Higher concentration of solutes (substances dissolved in a liquid) outside the cell

Explain: Hypotonic Solution

- Hypotonic solution: Lower concentration of solutes outside the cell

Explain: Isotonic solution

- Isotonic solution: Equal concentration of solutes inside and outside the cell

Explain what happens if an animal cell is placed in a concentration salt or sugar solution (hypertonic solution)

Water will leave the cell by osmosis, and as a result, the cell will shrink and shrivel up

Explain what will happen if an animal cell were to be placed in a solution with a solution with the same concentration as that inside of the cell (isotonic solution)

There will be no net movement, cell remains the same (in other words the same amount of water that enters cell, exits cell)

What happens if an animal cell is placed in a dilute solution or water (hypotonic solution)

Water will enter the cell by osmosis. As a result, the volume and pressure inside the cell will increase and the animal cell will swell up and eventually burst. This is known as cell lysis

In the case of animal cells what conditions is the most ideal

Isotonic conditions

What would happen if a plant cell was placed in a concentrated sugar or salt solution (hypertonic solution)

Water will leave the cell by osmosis.

Plant cell loses water and becomes flaccid.

The cell membrane and the cytoplasm pull away and detach from the cell wall. This is known as plasmolysis

This is usually what causes wilting plants

What would happen if a plant cell was placed in a solution with the same concentration as the inside of the cell (isotonic solution)

There will be no net movement of water and the cytoplasm just presses against the cell wall. The plant cell is flaccid.

What happens if a plant cell is placed in a dilute solution or water - solution that is less concentrated than the concentration of the cell - (hypotonic solution)

Water will enter the cell by osmosis

The cytoplasm pushes hard against the cell wall and the cell becomes turgid, maintaining the rigidity and stability of the cell.

When a cell is turgid, it exerts

A turgor pressure on its neighboring cell

What is a turgor pressure and what does it provide for the plant

the pressure of water pushing plasma membrane against the cell wall providing support and structure to the plant

Which condition is the ideal for a plant cell and why

A hypotonic extracellular solution is ideal because the plasma membrane can only expand to the limit of the rigid cell wall, so the cell won’t burst.

What is reverse osmosis

A way to purify water

Reverse osmosis is

reversing the natural process of osmosis

Is reverse osmosis important in Malta, why?

Yes because Malta is at risk of desertification

How does reverse osmosis work

By pushing water through a special filter that blocks impurities and only lets clean water pass through

What can reverse osmosis be considered as

A process of active transport

Sometimes dissolved molecules are at a higher concentration inside the cell than outside but the organism needs these molecules so they still must be absorbed T/F

True

What is active transport

The movement of particles through a partially permeable membrane requiring energy

What movement does it involve

The movement of dissolved molecules across a partially permeable cell membrane from a region of lower concentration to a region of higher concentration, against the concentration gradient and therefore requires energy from respiration to take place.

When is the energy used in active transport released

during the process of respiratation

What are special proteins, found in cell membranes known as

carrier proteins

What do carrier proteins do

pick up specific molecules and take them through the cell membrane against the concentration gradient

Can these also be used

Yes

In humans, when/where does active transport take place

During the digestion of food in the small intestine

What happens during this process

• Carbohydrates are broken down into simple sugars such as glucose

• The glucose is absorbed by active transport into the villi, to be passed into the bloodstream and taken around the body.

Give an example of active transport in plants

Mineral ions are taken up by root hair cells from the soil by active transport