A higher outside air temperature reduces the angle and rate of climb

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It is the Net movement of molecules from a region of high concentration  to a region of low concentration. It is a passive cell movement and they do not need to use energy to move.

Concentration gradient: the difference between the concentration of molecules in two places.

Factors that affect diffusion:

  • Distance molecules have to travel (the shorter the better)

  • Concentration gradient (the bigger the better)

  • Surface area (the larger the better)

  • Temperature (more kinetic energy at higher temperatures)

  • Size of molecule (the smaller the better)


It is a special type of diffusion. It is the passage of water molecules from a region of high concentration to a region of lower concentration by passing through a partially permeable membrane.

Solution = Solute + Solvent

Osmosis and animal cells

Animal cells burst in pure water. Water molecules diffuse into the cell through the partially permeable membrane.

Animal cells will shrink in concentrated solutions. Water diffuses out of the cell through the partially permeable membrane.

Osmosis is potentially damaging to animal cells because they can burst.

Osmosis and plant cells

If water enters the plant cell, the cytoplasm will swell but will not burst. If water leaves the cell, cytoplasm will shrink and dry up.

Plant Nutrition

Photosynthesis: it is a fundamental process in which plants manufacture carbohydrates from raw materials using sunlight energy.

FORMULA: 6CO2 + 6H2O --- sunlight, chlorophyll → C6H12O6 + 6O2

Process of photosynthesis

Green plants take in CO2 through their leaves (DIFFUSION). Water is absorbed through the roots (OSMOSIS) and transported to the leaves through xylem vessels. Chloroplasts with chlorophyll trap light energy which breaks up water molecules and forms glucose. Glucose is usually changed to sucrose for transport or starch for storage. Oxygen is released as a waste or used by the plant for respiration.

Factors limiting photosynthesis

  1. Light intensity - photosynthesis increases with brighter light but only up to a point. When the point is reached, the rate of photosynthesis stays constant. Chloroplasts cannot trap any more light.

  2. CO2 concentration - Higher Co2, the faster rate of photosynthesis. Air has about 0.04% CO2. The rate of photosynthesis increases up to a point and then remains constant because another factor becomes limiting.

  3. Temperature - The rate of photosynthesis decreases at higher temperatures because enzymes in chloroplasts are denatured.

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