Summary of OCR AS-Level Biology B

Biology Revision Notes - Five Kingdoms:

 Five Kingdoms:
o Fungi
o Plantae
o Animalia
o Protoctista
o Prokaryotae
 Prokaryotae:
o Organisms which do not have a membrane bound nucleus
o MOST reproduce via BINARY FISSION – cells grow, DNA
replicates and cell divides into two
 Fungi:
o All are HETEROTROPHIC – complex organic molecules are
broken down to simpler ones
o Cell walls are made of – CHITIN
o Store CARBOHYDRATE in the form of – GLYCOGEN
o Show LITTLE TISSUE DIFFERENTIATION which means there
are no distinct organs
o EXTRACELLULAR DIGESTION – HYPHAE
 Plantae:
o All are AUTOTROPHIC – simple inorganic molecules are used
to make more complex organic molecules
o Sub-divided into two main groups:
 NON-FLOWERING e.g. MOSSES and ferns
 FLOWERING e.g. trees, grasses, blue bells
o Cell walls are made of – CELLULOSE
o Show TISSUE DIFFERENTIATION into roots, stem and leaves
o Contain CHLOROPHYLL
o Store CARBOHYDRATE in the form of STARCH
 Animalia:
o All are HETEROTROPHIC – complex organic molecules are
broken down to simpler ones
o Multicellular, don’t have CELL WALLS
o Contain specialised cells and tissues e.g. NERVOUS and
MUSCLE TISSUES
o TISSUE – collection of similar cells with a common function
o Store CARBOHYDRATE in the form of – GLYCOGEN

,Biology Revision:
Homeostasis:

 Homeostasis – maintaining internal conditions within narrow limits
 Usually involves – negative feedback,
 Effectors – are either muscles or glands, they bring about response
to a stimulus
 Receptors – detect stimuli e.g. thermo receptors
 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.
 Thermo regulation - the regulation of body temperature
 Endothermic animals – warm blooded e.g. mammals, birds. These
produce lots of heat and retain what is required
 Exothermic animals – cold blooded e.g. reptiles, fish, and
amphibians. These produce less heat and retain very little of it.
 Short-term heat production – (1) shivering – rapid contraction and
relaxation of muscle fibres. Major disadvantage – uses lots of
energy (2) release of hormone adrenaline – from adrenal glands,
this raises the metabolic rate of the individual.
 Basal Metabolic Rate – energy expended by a resting fasting person
in a room at a comfortable temperate.
 Factors that effect metabolic rate:
 Age
 Sex
 Diet
 Activity
 Health
 Drugs
 Long-term heat production – increased production of the hormone
thyroxine from the thyroid gland in the neck.
 Heat loss:
 Radiation – loss of heat via electromagnetic waves
when body is warmer than the surroundings.
 Evaporation – mainly via sweating
 Conduction – the loss of heat through contact with an
object/medium that is cooler than the body
 Regulation of heat loss:
 Vasoconstriction and vasodilatation – alter blood flow
to the skin and hence regulate heat loss by changing
the diameter of the arterioles in the skin
 Vasodilatation – widening of arterioles, increase blood
flow
 Vasoconstriction – narrowing of arterioles decrease
blood flow
 Erector pili muscle – reduce heat loss the muscles contract causing
hair to stand upright. This traps a still layer of air close to the skin
and reduces heat loss.
 Adipose tissue – fat storage tissue
 Hot and cold thermo-receptors in the skin send nerve impulses to
the hypothalamus which brings about the changes necessary to
restore the correct temperature.

, 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
 ENVIROMENTAL CONDITIONS faced by each group
DIFFER, the SELECTION PRESSURES on each group also
DIFFER
 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
groups
o Speciation:
 Eventually the genetic/phenotypic differences between
members of the separated groups becomes so great that
they CANNOT INTERBREED TO PRODUCE FERTILE
OFFSPRING, this means a new species has been produced