Biology Revision Notes - How Natural Selection May Lead To Speciation

AQA Biology, Energy and Continuity - Speciation

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How natural selection may lead to speciation:
Species ­ Organisms that reproduce to produce FERTILE offspring
Population ­ Group of organisms of the same species found in the
same place (habitat) at the same time
Mechanisms which may lead to speciation:
o Isolation:
Physical isolation ­ continental drift, deforestation,
mountain range, volcanic activity, floods. Road building
Reproductive isolation ­ sexual selection, reproducing at
different times of year
o Natural Selection:
Some genetic variation between separated groups
RANDOM mutations occur within each group leading to
further genetic variation between groups
DIFFER, the SELECTION PRESSURES on each group also
The individuals in the two groups may start to occupy
different NICHES
Over an EXTENDED period of time, through MANY
generations, there will be different CHANGES IN the
ALLELE and phenotype FREQUENCIES in the separated
o Speciation:
Eventually the genetic/phenotypic differences between
members of the separated groups becomes so great that
OFFSPRING, this means a new species has been

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Metabolic Pathways:
Anabolic ­ makes larger molecules from smaller ones and store
energy e.g. photosynthesis
Catabolic ­ break down larger molecules to smaller ones. They
release energy e.g. respiration and digestion
Rate Determining or Rate Limiting step ­ slowest step
Negative Feedback - departure from a set level is detected by
receptors. These send information to effectors which bring about a
return to the original value.…read more

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Aerobic respiration:
o Occurs in the cytoplasm
o Initial Substrate ­ glucose
o Final products ­ 2 pyruvate, 2 ATP, reduced NAD
Link Reaction:
o Links Glycolysis in the cytoplasm with Krebs cycle in the
o Decarboxylation ­ loss of carbon
Krebs Cycle:
Take place in the matrix of the mitochondria
Acetyl CoA from the link reaction donates TWO ARBON MOLECULES
which combines with a 4 CARBON MOLECULE to produce a molecule
with 6 CARBONS…read more

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Basic Leaf Structure:
Functions of:
o Cuticle ­ reduces water loss through leaf surface
o Xylem ­ transports water and mineral ions (potassium)
o Phloem ­ transports sucrose and other solutes
o Sucrose = glucose and fructose
o Upper epidermis is colourless ­ so sunlight can reach the
chloroplast in palisade mesophyll cells
o Air spaces in spongy mesophyll ­ large internal surface area for
gas exchange
o Stroma ­ site of light independent stage of photosynthesis
o Thylakoids ­ site of light dependent stage…read more


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