Transcript B2 revision presentation File

B2 in a lesson
Cell Parts:
Bacteria Cells:
Yeast Cells:
Cells may be specialised for a particular function.
Their structure will allow them to carry this function
out.
Cell
Job
Adaptations
Leaf
cell:
absorbs light for
lots of chloroplasts
photosynthesis
Root
hair
cell:
absorbs water
finger like shape for large
and mineral ions surface area
Sperm
cell:
fertilises an egg
head contains an enzyme
to help penetrate egg
Red
blood
cell:
carries oxygen
to the cells
thin outer membrane so
oxygen diffuses easily
Diffusion:
Net movement of particles from an area of high
concentration to an area of low concentration.
A tissue is a group of specialised cells that have a
similar structure and function.
Tissue
Function
Muscular tissue
Contracts, bringing about movement
Glandular tissue
Produces substances such as enzymes and
hormones
Epithelial tissue
Covers some parts of the body
cells  tissues  organs  organ systems
Organ systems are groups of organs that carry out a
particular function. For example, the digestive system:
Leaves are adapted to absorb sunlight for photosynthesis
Three factors can limit the speed of photosynthesis:
• light intensity
• carbon dioxide concentration
• temperature
Farmers can use their knowledge of limiting factors on
photosynthesis to increase crop yields.
• Artificial light – extends time for photosynthesis
• Heating – increases the rate of photosynthesis
• Adding carbon dioxide (CO2) – increases the rate
The cost of providing extra lighting, heat
and carbon dioxide has to be weighed
against the increased crop yield and the
extra income it will provide.
Tip: paraffin lamps provide light,
heat and CO2!
Glucose is produced during photosynthesis and is
used by the plant to make:
• Cellulose - which strengthens the cell wall
• Proteins - such as enzymes and chlorophyll
Glucose is stored by plants as starch, fats and oils.
The distribution of living organisms in a particular
habitat may be affected by physical factors, such as:
•
•
•
•
•
Temperature
Amount of light
Availability of water
Availability of nutrients
Availability of oxygen and carbon dioxide
Sampling: Quadrat
• Square frame
• Used to sample a small area
• Samples chosen at random
Sampling: Along a Transect
•
•
•
•
Not random
Tape stretched between two points
Samples taken along the line using a quadrat
Shows how the distribution of organisms changes along
the line
Enzymes
• Biological catalysts: speed up reactions.
• Enzymes are protein molecules, and so are made up
of amino acids.
+
enzyme
+
reactant
↔
↔
enzyme-reactant
complex
↔
↔
+
enzyme
+
products
Factors that affect enzymes:
• At lower temperatures
rate of reaction is slow
• Over 40 C enzymes
are denatured
• Active site shape is
altered, therefore
cannot fit substrate
• If pH is too far from
optimum, enzyme will
be denatured so
active site will not fit
substrate.
Digestive Enzymes:
Enzyme
Made by
Works in
Substrate
Product
Conditions
Amylase
Salivary
glands,
pancreas,
SI
Mouth & SI
Starch
Glucose
Neutral
Protease
Stomach,
pancreas,
SI
Stomach,
SI
Protein
Amino
Acids
Acid
Lipase
Pancreas,
SI
SI
Lipids
Fatty Acids
& Glycerol
Neutral
What do enzymes do for us?
Industry
Function of enzymes
confectionery
(sweets)
change glucose into fructose, which is sweeter so
less is needed and is used in 'slimming' foods
(isomerase).
baby food
start off digestion of food (proteases and lipases)
biological
detergent
break down stains (proteases and lipases).
Aerobic respiration (with oxygen)
glucose + oxygen → carbon dioxide + water (+
energy)
When too little oxygen reaches the muscles during
exercise, they use anaerobic respiration to obtain
energy.
Anaerobic respiration (without oxygen)
glucose → lactic acid (+ energy)
Where is the genetic information in a cell?
• Inside each cell is a nucleus.
• Inside the human nucleus are 46 chromosomes (two
sets of 23, one set from Mum, one set from Dad).
• Chromosomes are made from DNA.
• A section of DNA is called a gene.
Mitosis
The genetic material is copied
The cell divides once to form two genetically
identical body cells
Mitosis is used for growth or to replace cells.
Meiosis
Forms gametes (sex cells).
The cell divides twice to form
four gametes.
Each daughter cell
contains half of the
chromosomes of
the original cell.
Stem Cells
Unspecialised - they can become any type of cell in the
human body.
As the cells of an embryo divide (by mitosis) and the
embryo develops, the cells become differentiated.
Fossils:
• Evidence of early life
• Formed from:
– Hard parts of animals that don’t decay
– Parts of animals that haven’t decayed because
conditions needed for decay are absent
– Parts of organism are replaced by minerals
– Preserved traces of organisms (footprints etc)
The fossil record is incomplete.
Why?
•
•
•
•
Early forms of life were soft bodied.
Fossilisation requires very specific conditions.
Many fossils are destroyed.
Many fossils have not been found yet.
Evolution by Natural Selection
Individuals in a species show a
wide range of variation.
This is because of differences
in genes.
Individuals most suited to the
environment are more likely to
survive and reproduce.
The successful genes are then
passed to the offspring in the
next generation.
Charles Darwin
Extinction
What causes organisms to become extinct?
•
•
•
•
Competition
New predators
New diseases
Environmental changes
Why did the dinosaurs become extinct?
Volcanoes
Rocks formed by huge eruptions 65 million years ago can
be found in India today.
Meteorite Impact
The remains of a 180km-wide crater caused by a
meteorite 65 million years ago can be found near
Mexico.
Disease
This theory doesn’t explain why so many sea animals
died at the same time.