Define diffusion and describe the role of diffusion in nutrients uptake and gaseous exchange in plants and humans.

Define osmosis and describe the effects of osmosis on plant and animal tissues.

Define active transport and discuss its importance as an energy-consuming process (Pure)

•Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient.

•The difference in concentrations of the substance between the two regions is known as concentration gradient or diffusion gradient.

Under normal

condition…

Dissolved substance diffuse throughout liquid in which they are dissolved.

How does the ‘water baby’ works?

Examples of diffusion:

Carbon dioxide diffuses from blood capillary into alveoli and oxygen diffuses from alveoli into surrounding blood capillaries.

The diffusion of carbon dioxide through the stomata into the mesophyll cells.

The diffusion of water vapour from the leaves during transpiration.

Osmosis is …

• the net movement of water molecules

• from a region of higher water potential to a region of a lower water potential

• through a partially permeable membrane

• Involves only water molecules

Concentrations of Solutions Dilute solutions:

- larger number of water molecules (solvent) compared to another similar solution.

- dilute solutions have a higher water potential, compared to another similar solution.

- Eg) 5% sugar solution means:

5% sugar molecules;

95% water molecules

Concentrated solutions:- smaller number of water molecules (solvent) compared to another similar solution.- concentrated solutions have a lower water potential, compared to another similar solution.- Eg) 10% sugar solution means:

10% sugar molecules;90% water molecules

QUESTION:

Compare between a 5% and 10% sugar solution.

Which one has a higher water potential?

Osmosis Sugars such as starch molecules CANNOT

pass through the partially permeable membrane (Too big)

However, sugar such as glucose CAN pass through the partially permeable membrane (Small enough)

Partially permeable membrane

Higher water potential

Lower water potential

Another example of osmosis5% sucrose solution10% sucrose solution

Partially permeable membrane

Point A Point B

Demonstrations of Osmosis

Question:

What will happen to the water level in glass tube?

Increase.Water enters the visking tubing by osmosis. The Visking tubing swells and becomes firm and turgid.

The surrounding solution has a higher water potential than the solution in the visking tubing.

Decrease.Water leaves the visking tubing by osmosis. The Visking tubing shrinksand becomes soft and flaccid.

Surrounding solution has a lower water potential than the solution in the visking tubing.

Water level and Visking tubing remain unchanged. No net movement of water molecules into and out of the visking tubing.

The surrounding solution has the same water potential as the solution in the visking tubing.

Describe the changes that took place in the water levels of the solution in the glass tube and beaker.

MicroQues 1

Decrease. Water leaves the Visking tubing by osmosis. The Visking tubing shrinks and becomes soft.

Dilute solution

= ____water potential

Concentrated solution = ____ water potential

high

low

MicroQues 1

Both involves movement of substances.

Both involves movement of substances from a region of its higher concentration to a region of lower concentration.

Both involves movement of substances down a concentration gradient.

MicroQues 2(a)

State the similarities between osmosis and diffusion.

MicroQues 2(B)

State two differences between osmosis and diffusion.

DiffusionOsmosi

s

Both involve the movement of molecules

from a region of their higher concentration

to a region of their lower concentration

How are they alike?

1. Involves movement of all types of molecules.

2. Do not involve a partially permeable membrane

1. Involves movement of only water molecules

2. Involve the movement of water molecules passing through a partially permeable membrane

How are they different?

Quiz Time

1. Which of the following processes causes juice the chilli to curl outwards?

a. Diffusion

b. Transpiration

c. Osmosis

d. Plasmolysis

Watch video: Chilli bloom practical

Quiz Time2. How could a lettuce, which has just wilted,

be made firm and crispy again?

a. Submerge in water

b. Submerge in a 20% sugar solution

c. Submerge in a 30% sugar solution

d. Submerge in a 50% salt solution

The cell membrane of living cells are partially permeable.

The cell wall, however, is non-living, tough and fully permeable.

In a plant cell, the vacuole membrane (tonoplast) is also partially permeable.

The cell sap in the large central vacuole of a plant cell is highly concentrated (low water potential) as it contains a complex mixture of substances.

Cells in a Solution with High Water Potential

Water enters the cell by osmosis.

Plant cell

Vacuole increases in size. Plant cell becomes firm and turgid.

Animal cell

Animal cell swells and may burst. Why?

Why animal cell will burst? Due to the absence of a cell wall. Cell wall is strong and relatively inelastic.

Cells in a Solution with Low Water Potential

Water leaves the cell by osmosis.

Plant cellVacuole decreases in size and cell becomes soft and flaccid.

Cytoplasm shrinks away from cellulose cell wall, through a process known as plasmolysis.

Watch animation: Plant cell when placed in low/high water potential

Cells in a Solution with Low Water Potential

Animal cellThe animal cell shrinks.

Little spikes appear on the plasma membrane. This process is called crenation.

Watch animation: Animal cell when placed in low/high water potential

Importance of turgor pressure in plants

• Help maintain shape of soft tissues in plants, especially young stems and leaves

• Changes in movement of plants due to turgor• Plasmolysed leaves are flaccid and the cells

can die

MicroQues 3Four plant cells were placed in 20% sucrose solution, 50% sucrose solution, 80% sucrose solution and pure water separately.

In the table below,(a) describe the appearance of the plant cells.(b) identify the solution that the cells have been placed in.

Pure water 20% sucrose 50% sucrose 80% sucrose

Cell become turgid.

No change. Cell become flaccid.

Cell become plasmolysed.

MicroQues 3

Question

What happens to animal

and plant cells when placed

in solutions with differing

water potentials?

Active Transport (PURE) Requires energy When substances move from a region of

lower concentration to a region of higher concentration against a concentration gradient

Occurs only in living cells as only living cells respire

Respiration will release energy where part of it will be used in active transport

Active transport is the process in which particles move from a region of low

concentration to a region of high concentration, against the concentration

gradient, with the use of energy.

Examples of active transport:

The absorption of mineral salts from the surrounding soil solution by root hair cells.

The absorption of glucose and amino acids by the epithelium cells in the small intestines of man, when they are low in concentration.

Which of the following diagram illustrates the most likely appearance of a red blood cell that has been placed in distilled water?

Micro Ques 4

( D )

A strip of potato, originally 50 mm in length, was measured after it was soaked in distilled water. Which of the following graphs A, B, C or D best represents the results?

Micro Ques 5

( A )

length of potato strips/mm

The apparatus shown in the diagram was set up. After one hour, the water in the beaker turned red. What is the most likely reason for this colour change?

Micro Ques 6

A Molecules of red ink move through the membrane by diffusion.B Molecules of red ink move through the membrane by osmosis.C Molecules of water move through the membrane by diffusion.D Molecules of water move through the membrane by osmosis.

( A )