Principles of Organisation and Transport in Cells

cell

The basic building block of a living organism.

tissue

A group of cells with a similar structure and function working together. For example, muscular tissue contracts to bring about movement.

organ

A collection of tissues working together to perform a specific function. For example, the stomach contains glandular, muscular and epithelial tissues.

organ system

A group of organs working together to perform specific functions. For example, the digestive system contains organs such as the stomach, the small intestine and the large intestine.

Diffusion

The net movement of particles from an area of higher concentration to an area of lower concentration.

Factors affecting diffusion rate

●Concentration gradient - larger gradient, faster diffusion. ●Temperature - higher temperature, faster diffusion. ●Surface area - larger surface area, faster diffusion.

Substances transported by diffusion in lungs

●Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient.

Substances transported by diffusion in kidney

●Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine.

Adaptation of single-celled organisms for diffusion

They have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs.

Surface area to volume calculation

Surface Area = Number of Sides x (Side Length x Side Width) Volume = Length x Width x Depth Ratio = Surface Area:Volume

Factors increasing gas exchange effectiveness

●Large surface area ●Thin membrane (short diffusion path) ●Efficient blood supply (animals) ●Ventilation (animals)

Osmosis

The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Isotonic solution to a cell

The concentrations of the external and internal (inside cell) solutions are the same.

Hypertonic solution to a cell

The concentration of the external solution is higher than that of the internal solution (inside cell).

Hypotonic solution to a cell

The concentration of the external solution is lower than that of internal solution (inside cell).

Effect of hypotonic solution on animal cell

Water moves into the cell, causing it to burst.

Effect of hypertonic solution on animal cell

Water moves out of the cell, causing it to shrivel up.

Turgor pressure in plants

Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall.

Effect of hypertonic solution on plant cell

Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size. The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed.

Active transport

The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration.

Active transport in root hair cells

Root hair cells use active transport to take up mineral ions from a more dilute solution in soils. Ions such as magnesium and nitrates are required for healthy growth.

Active transport in digestion

Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood. Glucose is then transported to the tissues where it can be used in respiration.