Cells
The smallest unit of life. All living things are made from cells.
Animal cells, have the following parts:
-nucleus
-cytoplasm
-cell membrane
-mitochondria
-ribosomes
Plant cells also have:
-cell wall
-chloroplasts
-permanent vacuole
Nucleus
Controls the activities of the cell.
Cytoplasm
Where most of the chemical reactions take place.
Cell membrane
Controls the passage of substances in and out of the cell.
Mitochondria
Where most energy is released in respiration.
Ribosomes
Where protein synthesis occurs.
Cell wall
Strengthens plant cells.
Chloroplasts
Absorb light energy to make food in plant cells.
Permanent vacuole
Filled with cell sap in plant cells.
The chemical reactions inside cells are controlled by enzymes. Examples:
-enzymes for respiration are in the mitochondria
-enzymes for photosynthesis are in the chloroplasts
-enzymes for protein synthesis are on the ribosomes
Specialised cells
Carry out a particular function.
A root hair cell...
has a large surface area to absorb water and minerals easily.
A palisade cell...
has many chloroplasts for photosynthesis.
A white blood cell...
can change its shape to engulf microbes.
A sperm cell...
has a tail to swim to the egg.
A nerve cell...
has a long nerve fibre to carry messages to other cells.
Tissue
A group of similar cells carrying out a particular function.
Organ
A group of different tissues carrying out a particular function.
System
A group of different organs carrying out a particular function.
Examples of cells:
Nerve, ciliated epithelial, root hair and palisade
Examples of tissues:
Nervous, epithelium, epidermal and mesophyll
Examples of organs
Spinal cord, trachea, lateral root and leaf.
Examples of organ systems:
Nervous, breathing, root and shoot
To get into or out of cells...
dissolved substances have to cross the cell membranes.
Solutes
particles in solution eg. glucose, sodium ions, chloride ions.
Solvent
liquid in which the particles are dissolved eg. water.
Solute and solvent molecules...
move around randomly.
Solutes can move into and out of cells...
by diffusion and osmosis.
Diffusion
The spreading of the particles of a gas or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration.
Oxygen required for respiration...
passes through cell membranes by diffusion.
Differences in the concentrations of the solutions inside and outside a cell...
cause water to move into or out of the cell by osmosis.
If there is a higher solute concentration on one side of a membrane...
water will move in that direction.
Osmosis in animal cells:
If animal cells are placed in a solution that has a higher solute concentration than the cytoplasm, then water will leave the cell by osmosis, until it shrinks and dies. If animal cells are placed in a solution that has a lower solute concentration than t
Osmosis in plant cells:
If plant cells are placed in a solution that has a higher solute concentration than the cytoplasm, then water will eave the cell by osmosis, and the cell
membrane separates from the cell wall (plasmolysis). This will cause a
plant to wilt.
If plant cells
Photosynthesis
Photo = light
Synthesis = making of (glucose)
Photosynthesis = making glucose using light
Complex definition of photosynthesis:
A process in green plants that produces complex organic chemicals (glucose) from simple inorganic chemicals (carbon dioxide and water) using light energy.
Photosynthesis in more detail:
1. Light energy is absorbed by a green substance called chlorophyll.
2. Plants look green because chlorophyll reflects green wavelengths of light.
3. The plant then uses this energy for photosynthesis.
4. Light energy is used to convert carbon dioxide and
Word equation for photosynthesis:
Carbon dioxide + water (+ light energy and chlorophyll) ? Glucose + Oxygen
Chemical equation for photosynthesis:
6 CO2 + 6 H2O ~~ C6 H12 O6 + 6 O2
Where does photosynthesis happen?
-Leaves are the main site of photosynthesis.
-Photosynthesis mainly occurs in the mesophyll cells.
-These cells contain lots of chloroplasts.
-Chloroplasts contain chlorophyll.
Two types of mesophyll cells:
-Palisade cells absorb most light.
-Spongy cells absorb the rest.
Factors that limit the rate of photosynthesis:
1. Temperature - a low temperature will limit the rate as the molecules will move less and therefore the reaction happens slower.
2. Carbon dioxide - a shortage of carbon dioxide will limit the rate as fewer molecules will be available for the reaction.
3
Farmers artificially manipulate...
the environment in which they grow plants.
They grow plants in...
greenhouses or in polythene tunnels.
They can control the temperature...
in greenhouses using heaters and ventilation.
They can artificially increase...
the carbon dioxide levels.
They can control the light...
using fluorescent lamps.
By doing this...
their plants grow faster and certain plants can be grown in this country out of their natural growth season. Therefore, they increase their profits.
How do plants use glucose?
The glucose produced in photosynthesis may be converted into insoluble starch for storage. Plant cells use some of the glucose produced during photosynthesis for respiration.
Why do plants need minerals?
Plant roots absorb mineral salts including nitrates needed for healthy growth.
For healthy growth plants need mineral ions including:
-nitrate - for producing amino acids which are then used to form proteins.
-magnesium - which is needed for chlorophyll p
Radiation from the Sun...
is the source of energy for most communities of living organisms.
Green plants capture a small part of...
solar energy which reaches them. This energy is stored in the substances which make up the cells of the plants.
Food chain
a diagram to represent feeding relationships between organisms, showing direction of energy flow.
Food web
a diagram that represents all of the feeding relationships between organisms in an ecosystem.
At each stage in a food chain...
less material and less energy are contained in the biomass of the organisms.
The amounts of material and energy contained in the biomass of...
organisms is reduced at each successive stage in a food chain because:
-some materials and energy are always lost in the organisms' waste materials.
-respiration supplies all the energy needs for living processes, including movement.
-much of this energy
Pyramids of numbers
Diagrams that display the numbers of organisms at each trophic level in a food chains. Each block is drawn to scale. These do not necessarily represent amount of biomass.
Pyramids of biomass
The biomass at each stage can be drawn to scale and shown as a pyramid of biomass.
All pyramids of biomass are pyramid shaped. The mass of living material (biomass) at each stage in a food chain is less than it was at the previous stage.
Biomass
mass of living material