Movement of Substances Across a Plasma Membrane in Living Organisms

3.3

Movement of Substances Across a Plasma Membrane in Living Organisms

Active Transport and Passive Transport in Living Organisms

Passive Transport

Passive transport in organisms occurs during:
- gaseous exchange between alveolus and blood capillaries through simple diffusion
- reabsorption of water occurs by osmosis through renal tubule in the kidney
- absorption of water by a plant root through osmosis
- absorption of fructose molecules in the villus by facilitated diffusion

Active Transport

Active transport in organisms occurs during:
- absorption of glucose and amino acids in th villus
- reabsorption of glucose through renal tubule in the kidney
- transport of sucrose from a leaf to a phloem tissue
- absorption of mineral ions by a plant root hair cells

Isotonic Solution

A solution that has the same concentration of solutes with the concentration of water

Hipotonic Solution

A solution that has a low concentration of solutes

Hypertonic Solution

A solution that has a high concentration of solutes

The Effects of Hypotonic Solution, Hypertonic Solution and Isotonic Solution on Animal Cells

Effects of Hypotonic Solution

When red blood cells are placed in a hypotonic solution, the water diffuse into the cells through osmosis, causing the cells to swell and finally burst
This is because the plasma membrane is to thin to withstand the osmotic pressure built up in the cell
The burst of red blood cells is known as haemolysis

Effects of Hypertonic Solution

When red blood cells are placed in a hypertonic solution, the water diffuse out of the cells through osmosis
This causes the cells to shrink
The red blood cells are said to undergo crenation

Effects of Isotonic Solution

Water diffuses into and out of the cells by osmosis at the same rate
No net movement of water across the plasma membrane
The cells maintain the normal shape

The Effects of Hypotonic Solution, Hypertonic Solution and Isotonic Solution on Plant Cells

Effects of Hypotonic Solution

When the plant cells are places in the hypotonic solution, water diffuses into the vacuole by osmosis
This causes the vacuole to expand and push the cytoplasm and plasma membrane against the cell wall
In this state, the cells are said to be turgid
Plant cells does not burst because the cell wall is rigid and strong
Turgor pressure is important to plant cells because it gives support and maintains the shape of cell
Cell turgidity causes the guard cell to swell to allow stomata to remain open for photosynthesis

Effects of Hypertonic Solution

When the plant cells are placed in the hypertonic solution, the water diffuse out from vacuole by osmosis
Vacuole and cytoplasm will shrink, causing the plasma membrane to be pulled away from the cell wall
This phenomena is known as plasmolysis
Plasmolysis causes the leaves and stems to bend downwards
Wilting occurs
Plasmolysed plant cells can regain their turgidity if the cells are returned to a hypotonic solution immediately
The cells are said to undergo deplasmolysis

Effects of Isotonic Solution

When the plant cell sap and the extracellular solution are isotonik, water potential is the same
The movement of water diffusion into and out of the cell is the same
Cells become flaccid