cells and cells physiology

Cells and the Chemicals of Life
The basic unit of all plants and animals.
Groups of cells which perform specialised functions are called tissues.
Groups of tissues which perform specialised functions are called organs.
To look at cells in the lab we use a light microscope. A much more powerful microscope is an electron microscope.


Structure of Cells
Living part called protoplasm surrounded by cell membrane.
Most cells have a nucleus which contains genetic information in the form of chromatin.
Protoplasm outside nucleus is called cytoplasm.
Small organs inside the cell that do specific jobs are called organelles.
Differences between Plant and Animal Cells

Animal Cells             Plant Cells
No cell wall               Cell wall
No chloroplasts        Chloroplasts
Small vacuoles         Large vacuoles


Cell Organelles
Mitochondria are common in very active cells (e.g. muscle cells) and they release the energy from food during respiration.
Ribosomes produce proteins (enzymes are proteins).
Chloroplasts are only found in plant cells, they contain chlorophyll (the photosynthetic pigment) and their job is photosynthesis.
Movement of substances
Cell membranes are selectively permeable and allow free movement of O2 and CO2 across them but restrict the movement of other molecules


Diffusion
The movement of a substance from an area of high concentration to an area of low concentration along a concentration gradient
Passive process (does not require energy)
CO2 and O2 move across the cell membrane by diffusion

Osmosis
Osmosis is the movement of water molecules across a semi-permeable membrane, from an area of high concentration of water molecules to an area of low concentration of water molecules.

Osmosis
Passive process (requires no energy)
The movement of water into plant cells is responsible for turgor pressure.
This pressure provides mechanical support to plants. Plants wilt when they lose turgor pressure
if plant cells lose water by osmosis then the cytoplasm shrinks and the cell undergoes plasmolysis.



Active transport
The movement of a substance from an area of low concentration to an area of high concentration against a concentration gradient

Active transport requires energy
An example of active transport: movement of nutrient ions from the soil solution (low concentration) into the root hairs (high concentration).