Movement in and out of cells

1. Movement in and out of cells

2. Movement into and out of cells • particles such as atoms, ions and molecules are always moving in and out of the cells • cells needs to take in nutrients such as glucose & amino acids • cells needs to get rid of metabolic wastes such as carbon dioxide & urea • substances move in and out of cell through processes such as: • diffusion; • osmosis & • active transport

3. Diffusion How Diffusion Works; • Diffusion is the net movement of molecules, from a region of their higher concentration to a region of their lower concentration i.e. down a concentration gradient as a result of their random movement

4. Importance of diffusion • solventis a substance in which another substance is dissolved • water is the major solvent in biological systems • soluteis the substance which dissolves in the solvent • glucose, oxygen & carbon dioxide are some of the most common solutes in biological systems • concentration gradient is the difference in concentrations of an ion or molecule between two places • concentration gradient is used to explain the movement of a substance from the inside to the outside of cell or from the outside to the inside of a cell • some major examples of diffusion in biological systems; • gas exchange at the alveoli of the lungs - oxygen diffuses from air to blood, carbon dioxide diffuses from blood to air, • gas exchange for photosynthesis in plants - carbon dioxide diffuses from air to leaf, oxygen diffuses from leaf to airthrough the stomata, • absorption of nutrients along the gut - glucose & amino acids diffuses from the small intestine into the blood, • absorption of water & dissolved mineral ions into the root hairs.

5. Osmosis How Osmosis Works; • Osmosis is the diffusion of water molecules from a region, of their higher concentration (with a dilute solution), to a region, of their lower concentration (with a concentrated solution) through a partially permeable membrane

6. Importance of osmosis • water is the medium of transport - everything transported in blood, phloem & xylem must be soluble in water • chemical reactions occur in water - cytoplasm is mostly water so reactions can occur • plants store water soluble substances such as mineral ions & sugars in cell vacuoles • some major examples of osmosis in biological systems; • absorption of water by plant roots, • reabsorption of water along the kidney tubules, • reabsorption of tissue fluid into the venule ends of the blood capillaries, • absorption of water along the alimentary canal -stomach, small intestine &the colon.

7. Importance of water potential gradient • water potential is the tendency for water molecules to move by diffusion from a dilute solution to a concentrated solution through a semi-permeable solution • water potential gradient is the difference in the concentration of water molecules • a dilute solution has a higher water potential & water molecules will tend to move from it, down a water potential gradient, into a concentrated solution • plant cells increase in size when placed in water because - water has a higher water potential than the inside of the cell, water diffuses into the cell down the water potential gradient by osmosis, the cell vacuole increases in volumepushing the cytoplasm and cell membrane against cell wall making the cell to swell – the cell becomes turgid • plant cells decrease in size when placed in concentrated salt solution because - a concentrated salt solution has a lower water potential than the cell contents, water molecules diffuses out of the cell down a water potential gradient by osmosis, the cell vacuole shrinks, pulling the cytoplasm and cell membrane away from the cell wall - the cell become plasmolysed

8. Turgor • Turgor is the pressure of the swollen cell contents against the cell wall when the external solution has higher water potential than the cell sap of the vacuole. • turgor pressure does not cause the plant cells to burst because of the presence of cell wall • role of turgor in plants; • mechanical support for soft non-woody tissue, e.g., leaves, • change in shape of guard cells forming the stomatal opening between them & • enlargement of young immature plant cells to mature size.

9. Active transport • active transport is the movement of ions in or out of a cell through the cell membrane, from a region of their lower concentration to a region of their higher concentration against a concentration gradient, using energy released during respiration • during active transport, special proteins within the cell membrane act as carrier proteins in cell membrane, they move ions or molecules against their concentration gradient into or out of the cell • carrier proteins change shape and this requires energy in form of ATP from respiration

10. Sodium-Potassium Exchange Pump

11. Importance of active transport • active transport is an energy-consuming process by which substances are transported against a concentration gradient • examples of active transport in biological systems includes; • uptake of mineral ions by root hairs • uptake of glucose & amino acids by epithelial cells of villi • reabsorption of glucose, amino acids and salts by the proximal convoluted tubule of the nephron in the kidney • cells that move ions against their concentration gradient such root hair cells has large number of mitochondria to produce energy required for active transport • factors such as oxygen concentration, glucose concentration & temperature which affect the rate of respiration also affects the rate of active transport

12. Cells and Life Processes