Biology GCSE transport in cells

What is diffusion

The passive net movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.

What is net movement

It is the overall movement of particles

Where have we seen diffusion before?

Oxygen and carbon dioxide during gas exchange in the alveoli of the lungs

What substance moves across the cell membrane in these organs?

Food molecules being absorbed into the bloodstream through the villo of the small intestine

What are the variables in this experiment?

" How does temperture affect the time taken for food colour to reach a state of equilibrium in a beaker of water?

Independant ( change ) : the temperature

dependent ( measured ) : the time taken to reach equilibrium

control ( stays the same)

- the quantity of dye

- type of container

- water

Method for How does temperture affect the time taken for food colour to reach a state of equilibrium in a beaker of water

1. Take two beakers. In one add hot water from the kettle and in another add cold water

2. place a small spatula of powdered dye in the hot water. Time how long it will take for the water to reach a state of equilibrum

3. Repeat this experiment with cold water

4. record your data in a table

How does temperature affect the rate of diffusion?

Correlation: The higher the temperature the faster the rate

Explanation

Particles have more energy so moves aroun faster

How does concentration gradient affect the rate of diffusion?

Correlation

The larger the concentration gradient the faster the rate

Explanation

Net movement from one side is greater

How does surface area affect the rate of diffusion?

Correlation

The larger the surface area the faster the rate diffusion

Explanation

More particles can cross through at once

How does Thickness of the membrane affect the rate of diffusion?

Correlation

The thinner the membrane the faster the rate of diffusion

Explaination

Shorter distance for particles to travel.

What molecules diffuse into and out of cells? 1st substance

Oxygen

1st movement - from air breathed into red blood cells in the lungs

2nd movement - Moves from red blood cells to body cells

What molecules diffuse into and out of cells? 2nd substance

Carbon Dioxide

1st movement - the body cells to blood plasma

2nd - the blood plasma to air breathed out in the lungs

What molecules diffuse into and out of cells? 3rd substance

Glucose

1st - small intestine to blood plasma

2nd - moves from blood plasma to body cells

What is accuracy

How close a measurement is to the true value

What is precision

How close the measuements are to eachother

What is validity

Are the values describing what was supposed to be measured.

How could you improve the validity of your results?

- Use a measuring cylinder with a higher resolution

- digital thermometer

- use a balance to masure the mass of the dye

How could you improve the precision of your results?

Perform repetitions and ensure results are similar to each other

How could you improve the accuracy of your results

Compare your results with the true values

What is the resolution of equipment?

The degree at which a piece of equipment can measure to

e.g. manual thermometer = 1 degree celcius +/-

digital thermometer = 0.1 degrees celcius +/-

digital thermometer has a higher resolution

What is a systematic error

A consistent repeated error. Usually due to faulty equipment or poor metodology

What is random error?

Unpredictable errors that are not repeated. Usually human error e.g. not measuring the correct amount once.

Does diffusion need a membrane to happen?

No, but in organisms it usually happens across a cell membrane

What is meant by adaptation?

Certain structures/features that allow organisms to perform a particular function

Diffusion occurs in many organisms where molecules or gas is exchanged name the exchange surfaces?

- small intestines

- alveoli in the lungs

- fish gills

- roots and leaves in plants

What improves the effectiveness of exchange surfaces

- having a large surface area

- a thinmembrane which ensures a short diffusion distance

( in animals ) an efficient blood supply

( in animals for gas exchange) being ventilated ( good circulation of air)

What creates a large surface area?

Many tiny villi create a large surface area - more particles can move across the membrane.

What does having a rich blood supply do?

Maintains a concentration gradient

as well as being well ventilated

Why does exchange becoe more difficult as the size and complexity of the organism increases?

As surface area to volume ration decreases diffusion becomes more difficult

solution :

exchange systems - increase the rate of diffusion

transport systems - reduce time taken for exchanged substances to reach cells.

How is red blood cell adapted for efficient gas exchange?

No nucleus, increases area to transport gases

Biconcave shape increases surface area

Contains haemoglobin which bonds with oxygen

Malleable shape to fit through small spaces.

What is osmosis

The net movement of water from an area of higher water concentration ( dilute solution) to an area of lower water concentration ( concentrated solution) through a partially permeable membrane.

What is a solute?

A dissolved substance in a solvent

What is a solvent?

A liquid used to dissolve a solute

what is a solution?

A liquid mixture in which the solute is uniformly distributed within the solvent

Solute + solvent = solution

What does a concentrated solution mean?

Less water

What does a dilute solution mean?

more water

What is water potential?

is pressure exerted by water molecules on a membrane and this pressure is measured in Kilopascals ( kPa)

What does a greater concentration of water in a membrane mean?

There is more kinetic energythe system has, therefore the greater the water potential energy.

Higher water potential means what for concentration and solution?

Low concentration of solute = dilute solution

There is a higher concentration of water

low water potential means what for concentration and solution?

High concentration of solutes = concentrated solution

lower concentration of water.

What is water optential in terms of osmosis?

The passive movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane.

What is hypertonic?

If the solution outside the cell has a lower water potential, we say it is hypertonic to the cell. Therefore water will move out the cell via osmosis.

Turgid?

A plant cell fully inflated with water

Plasmolysed

A plant cell that has lost water causing the cell membrane to be pulled away from the inside of the cell wall.

Flaccid?

A plant cell that is limp through a reduction of pressure inside the cell.

What is Lysis?

Bursting an animal cell by osmosis due to a lack of cell wall.

What will happen to the mass of a piece of potato when placed in a strong sugar concentrated solution and left for 24 hours?

There is a lower water potential outside the cell/ the solution is hypertonic in the cell

Meaning water will move out of the cell

via osmosis

therefore the mass of the potato will decrease, becoming flaccid.

Variables that effect osmosis

Temperature ( increasing)

Particles have more kinetic energy increasing the rate of omosis

Surface area of a cell - The larger the surface area the faster the rate of osmosis will occur, as more water molecules are able to collide with cell.

Concentration gradient - The greater the concentration gradient the faster the rate of osmosis.

Why do slugs not like salt?

Due to osmosis the slug's skin is the partially permeable membrane and the salt draws the water out of their bodies and dehydrated them. The salt becomes a solution when is mixes with the slugs mucus.

Descrive and explain what happens when plant cells are placed in solutions that are hypotonic ( dilute )?

The cytoplasm has a lot of solutes such as sugars and salts dissolved in it. When the cell is placed in a dilute solution ( higher water concentration) the net movement of water is into the cell. This causes the cell to swell. It does not burst because of the cell wall.

Describe and explain what happens when plant cells are placed in solutions that is isotonic ( balacned )?

When a cell is placed in a solution of same concentration as inside the cell, water moves in and out of the cell. There is no overall net movement of water.

Descrive and explain what happens when plant cells are placed in solutions that is Hypertonic ( concentrated) ?

When a cell is placed in a concentrated solution ( lower water concentration), the net movement of water is out of the cell. The cytoplasm pulls away from the cell membrane. The celll shinks.

Osmosis with a potato experiment variables?

independant variable - concentration of solution

Dependent variable - mass and length of potato chip

Control - same volume of solution, same length and thickness of potato chips, same potato, same amount of time in solution

Required potato osmosis practical.

1. Using a cork borer, cut three potato cylinders of the same diameter/length

2. Accurately record the mass of each potato cylinder using a scale.

3. Measure out a set volume of the distilled water, 0.5 mol/dm cubed and 1 mol/dm cubed sugar solution into 3 boiling tubes.

4. Add one potato cylinder to each test tube.

5. After 24 hours remove potatoes at the same time, pat down with tissue to remove excess water.

6. Record the new mass and calculate % change in mass.

Change in mass calculation

Original - new divided by original multiplied by 100.

Why the mass increased in boiling tube with the lowest sugar concentration?

- Water moved into th cell increasing mass from a higher water potential ( outside cell) to a lower water potential ( inside) via osmosis.

Why the mass decreased in boiling tube with the highest sugar concentration

- Water moved out of the cell decreasing mass from a higher water potential ( inside) to a lower water potential ( outside) via osmosis.

How could you find a more accurate concentration of sugar inside the potato?

Investigate smaller intervals of sugar concentration solutions

test ever 0.1 mol/dm cubed beterrn 1 - 0.5 mol/dm cubed.

What is active transport?

Active transport moves substances from an area of low concentration to an area of high concentration- against the concentration gradient, using energy from aerobic respiration ( made in the mitochondria)

Does active transport require energy?

Active transport requires energy, which is released via aerobic respiration in the mitochondria in the for of ATP ( adenosine triphosphate)

Describe the process of active transport from the inside of the cell to the outside of the cell.

The substance is at a low concentration outside the cell and high concentration inside the cell.

Sctive transport carried out by protein carriers.

The protein carriers are within the cell membrane, and they have a specific binding site for the extract molecule they are transporting.

The substance binds to the protein carrier on the side that it is at a low concentration

and using energy from respiration, the protein carrier releases the substance on the other side of the membrane - where it is already at a higher concentration.

Active transport in the gut

If the concentration of glucose in the gut is hihger than that of the blood diffusion will take place. However sometimes there is a lower concentration in the gut than in the blood. The concentration gradient is the wrong way- we coild loose glucose out of the blood and into the gut. So instead active transport takes place - this stops us from starving.

Explain how Nitrate ions, magnesium ions and water molecules will enter into the root hair cell.

The nitrate ions will enter via active transport

as the ions move against the concentration gradient into the cell

The magnesium ions will move into the cell via diffusion

from high to low concentration.

The water molecules move into the cell via osmosis

from high water potential to low water potential