bio, movement of substances

define diffusion

the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient

diffusion in our bodies

Body tissues are low in oxygen as it is used up for cellular respiration. During gaseous exchange, red blood cells transport oxygen to these body tissues.

The oxygen concentration in the red blood cells is higher than the oxygen concentration in the body tissues. This creates a concentration gradient, causing oxygen to move out of the red blood cells and into the body tissues.

define osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.

relationship between concentration and water potential

concentrated solution — lower water potential

dilute solution — higher water potential

when a plant cell is placed in a solution of higher water potential

cell expands and vacuole increases in size, since the cellulose of the cell wall is very strong and turgid, it prevents the cell from bursting so the cell becomes turgid

when a plant cell is placed in a solution of lower water potential

water moves out the cell, cell becomes flaccid. if cell continues to lose water, cytoplasm will shrink away from the cell wall, this is known as plasmolysis

when animal cell is placed in a solution of higher water potential

water enters the cell by osmosis, animal cell bursts due to absence of cell wall

when animal cell is placed in a solution of lower water potential

water moves out the cell by osmosis, cell shrinks, tiny spikes form on cell surface membrane, cell is crenated

define active transport

energy (from cellular respiration) is used to transport substances across a biological membrane against a concentration gradient

where does active transport occur?

Active transport occurs only in living cells because living cells respire. The energy used in active transport is from the energy used in respiration.

In Human body, examples of active transport include the uptake of glucose by microvilli of epithelial cells in the small intestine, and from the kidney tubules into the blood capillaries.

In plants, root hair cells can take in mineral salts form the soil solution by diffusion or active transport, depending on the concentration of mineral salts in the soil solution.