L

movement of substances

  1. define diffusion and describe its role in nutrition uptake and gaseous exchange in plants and humans

Definition 

  • The net movement of particles from a region of higher  concentration to a region of lower concentration down a concentration gradient, without requiring energy

Role in nutrition uptake 

In small intestine:

  • glycerol and fatty acids diffuse into the epithelium 

  • Glucose and amino acid are absorbed by diffusion into the blood capillaries of the villi

In root hair cells:

  • ions and mineral salts diffuse into the root hair cells

Gaseous exchange 

In lungs:

  • oxygen diffuses through the wall of the alveolus and the wall of the blood capillaries into the RBC

  • carbon dioxide diffuses from the blood into the alveolar air

In stomata:

During photosynthesis,

  • Carbon dioxide diffuses from the surrounding air into the intercellular air spaces in the leaf

  • Oxygen diffuses from the intercellular air spaces into the surrounding air

During respiration, 

  • carbon dioxide diffuses from the intercellular air spaces into the surrounding air

  • Oxygen diffuses from the surrounding air into the intercellular air spaces in the leaf

  1. define osmosis, investigate and describe the effects of osmosis on plants and animal tissues

Definition

  • The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane, without requiring energy.

Effects of osmosis on plant and animal cells

In a solution with higher water potential:

Plant cell, 

  • swells, become turgid

  • Vacuole increases in size & pushed the cytoplasm against the cell wall

  • Does not burst, protected by the inelastic cell wall

  • Turgor pressure: the pressure exerted by the water in the vacuole

Animal cells,

  • swell, may burst

  • Don’t have a cell wall to protect itself

In a solution with lower water potential:

Plant cells,

  • decrease in size, become limp or flaccid

  • Vacuole decreases in size

  • Cytoplasm shrinks away from the cell wall

  • Plasmolysis: shrinking of cytoplasm and cell membrane from the cell wall

  • Plasmolysed 

Animal cell,

  • shrinks, spikes appear on the cell, becomes crenated

  • Will eventually die of dehydration 

  • Crenation 

  1. Define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi.

Definition 

  • A process in which energy is used to move particles of a substance across a membrane against its concentration gradient from a region of lower concentration to a region of higher concentration.

Importance 

Root hair cells,

  • ions move into root hair cells via active transport if ion conc. in the soil is higher than in the cell

Villi (small intestine) , 

  • glucose and amino acids move into blood capillaries in the villi via active transport if glucose and amino acids conc. in the blood capillaries is higher than in the small intestine 

as in ion uptake by root hairs and uptake of glucose by cells in the villi.