Download GCSE Revision Booklet Biology Unit B1 Influences of life

GCSE Revision Booklet
Biology
Unit B1
Influences of life
Classification, Inheritance and variation
Classification
Each different organism (living thing) has a unique classification that gives it a
binomial (two word) name. E.g. dogs are called Canis familiaris in the binomial
system.
This system is divided into 7 divisions in a rank order they are:
Kingdom → phylum → class → order → family → genus → species
So dogs have the following classification:
Kingdom – Animalia (Animal)
Phylum – Chordata (vertebrate) – these are animals with a spine
Class – mammalia (mammal)
Order – Carnivora (Carnivores)
Family – Canidae
Genus – Canis
Species – familiaris
Use this phrase to help your remember the order Keep Plates Clean Or Family Gets Sick.
The five kingdoms are:
Animalia – all animals e.g. jellyfish, worms, chimpanzees
Plantae – all green plants e.g. ferns, moss, conifers and roses
Fungi – any fungus big or small e.g. moulds, yeast, mushrooms
Protoctista – only one cell but, with a nucleus e.g. amoeba & paramecium
Prokaryotes – only one cell but with no nucleus e.g. bacteria & blue-green algae
Scientists do not classify a virus as a living thing because they do not show all seven
processes for life.
The five chordate (vertebrate) groups are:
Fish – gills, fins, wet scales, external fertilisation
Amphibian – smooth skin, lungs or gills, external fertilsiation
Reptile – dry scaly skin, eggs with hard shells, internal fertilisation
Bird – wings, feathers, eggs with hard shells, internal fertilisation
Mammal – hair/fur on body, give birth to live young, feed young on milk, internal
fertilisation
A Species is a group of similar organisms that can interbreed and produce fertile
offspring.
A Hybrid is the infertile offspring that occurs, when two different species
breed/reproduce.
Evolution
Charles Darwin (1809 – 1882) proposed the theory of evolution that scientists accept
today.
Evolution is the slow, continual change of
organisms over a very long time. All living
things on the Earth have developed from the
first simple life forms that arrived
3,000,000,000 years ago.
One of the effects of evolution is that species will become better adapted to their
environment. If these species don‟t adapt they may become extinct due to being
unable to deal with any of these factors:
1) increased competition, 2) changes in the environment, 3) new diseases, 4) new
predators
My key observations:
 variation – in any population of organisms there will be some differences
 over-production – many organisms produce more offspring than survive to
adulthood
 struggle for existence – there is competition of survival and resources between
the organisms.
 survival – those with helpful characteristics are more likely to survive to breed
 useful characteristics – inherited by the offspring
 gradual change – of the species over a period of time as useful characteristics
are passed to offspring.
Darwin‟s theory of Natural Selection
1) Each species shows variation:
2) There is competition within each
species for food, living space, water,
mates etc.
3) The “better adapted” members of these
species, are more likely to survive –
“Survival of the Fittest” and reproduce.
4) These survivors will pass on their
better genes to their offspring who
will also show this beneficial
variation.
Evidence for Darwins theory
Fossil records – despite some gaps show how much (or how little) different
organisms have changed since life developed on Earth.
Antibiotic-resistant bacteria – bacteria reproduce rapidly and can evolve in a short
time, if the mutation (such as antibiotic resistance) is an advantage, they are more
likely to survive and evolve further.
DNA – Scientists can now examine the DNA of different species and see how closely
related they are to each other, e.g. Chimpanzees and humans share 96% of our
DNA
Adaptation
Every organism has certain features that allow it to survive in its habitat – so the
organism is adapted to its habitat, organisms living in different environments will
have different adaptations.
You need to be able to explain how organisms are adapted to survive in different
habitat extremes. You give the feature and then explain how it helps.
Artic or Antartic Environment
Animals
Thick layer of fat and fur- insulation against the cold
Small surface area to volume ratio – to minimise heat loss
A greasy coat, which sheds water after swimming.
White fur – to camouflage.
Large feet to prevent sinking in the ground
Plants
Grow close to the ground – stop it being blown by the wind
Have very small leaves – prevent water loss
Deep Sea Hydrothermal Vents
Thick layer of bacteria – to protect it from predators.
Makes a paper like tube – to hide it from predators
Variation
Variation means “differences” within a species”
Some of this variation is due to our parents “inherited variation”, but some of it is due
to our upbringing and the environment in which we live “Environmental variation”
Inheritance Only
Environmental Only
Blood Group
Natural Eye colour
Natural Hair Colour
Scars
Injuries
Both Inherited and
Environmental
Height
Weight
Some features in organisms show either continuous or discontinuous variation.
Continuous variation
Is a characteristic in any species that changes gradually over a range of values.
Examples include: height, weight, foot length etc So height ranges from the smallest person in the world to the largest person and all
the possible values in between.
A graph showing continuous variation will look like this (it is known as a bell shaped
curve or normal distribution) if you have data from a large sample size.
Discontinuous variation
A characteristic of any species with only a limited number of possible values.
Examples include: gender, blood group, eye colour
So human blood only has four possible values A, B, AB, or O)
A discontinuous graph looks like the one below, it will not form a bell shape.
Inheritance
All cells in the body (except the red blood cells) contain a nucleus which controls the
cell.
Chromosome Chromosomes are made
from long DNA molecules
The nucleus contains
chromosomes
gene
A gene is a short
section of DNA
Every persons DNA is unique (except for identical twins), this is why DNA can be
used to identify people.
Alleles
Different forms of the same gene are called alleles and they can be dominant or
recessive
 the characteristics controlled by a dominant allele develops if the allele is
present on one or both chromosomes in a pair
 the characteristic controlled by a recessive allele develops only if the allele is
present on both chromosomes in a pair
e.g. the genes controlling the hairline growth on a human forehead has a recessive
allele for a straight hairline and a dominant allele for a widows peak hairline.
In genetic diagrams a dominant allele will always be shown by a capital letter, while
the recessive allele is shown as a lower-case letter.
So if the genotype is WW or Ww the person will have a widows peak hairline, but if
the genotype is ww the person has a straight hairline. However the Ww genotype
displays a widows peak hairline, but they are carrying the allele for a straight hairline.
WW
W
Ww
ww
W
Ww
w
w
Ww
Ww
Note: WW is described as being homozygous for the dominant allele
ww is described as being homozygous for the recessive allele
Ww is described as being heterozygous
Cystic fibrosis
Cystic fibrosis (Cf) is caused by a recessive allele.
People with CF produce abnormally thick sticky mucus in their lungs and airways, so
sufferers are more likely to get respiratory diseases. If a child has CF then both
parents must either have CF or be carriers of the CF allele
Mother
father
F
f
F
FF
Ff
f
Ff
ff
.
Mother
father
F
f
F
FF
Ff
F
FF
Ff
Sicke cell disease
Sickle cell disease is another recessive conditions so the genetic crosses for it will
be similar to the ones above for Cystic fibrosis.
In Sickle cell anemia the red blood cells become misshapen and can stick together
which can block blood vessels. Sickle cell disease sufferers can become very tired
and quickly get out of breath. If the sickle cells block a blood vessel, this can be fatal.
Responses to a changing environment
Homeostasis
Homeostasis means “controlling internal conditions” using the nervous system and
hormones.
Waste products that need to be removed + how
CO2
Produced by respiration, removed via lungs
Produced by liver breaking down amino acids,
removed by kidneys and transferred to bladder
Urea
Internal conditions that need controlling + how
Temperature
Ion content
Water content
Increased by shivering, lost by sweating
Increased by eating, lost by sweating + urine
Increased by drinking, lost by sweating + urine
Blood Glucose
Increased and decreased by hormones
Controlling water content (Osmoregulation)
Water loss is controlled by water loss from
 the lungs, when we exhale (breathe out)
 the skin by sweating
 the body, in urine produced by the kidneys
Osmoreceptors in
pituitary
Less ADH is released
In the kidneys
Water Increases
Normal Water Level
Water Increases
Water Decreases
ADH is released
In the kidneys
Osmoreceptors in
pituitary
Controlling the Ions (salts) in the body
This is controlled to protect cells by avoiding too much water entering or leaving
them. Ion content is controlled by loss of ions from:
 the skin by sweating
 the body, in urine produced by the kidneys
Controlling body temperature (Thermoregulation)
Human enzymes usually work best at 37°C, this is our core body temperature.
High temperatures can cause dehydration, heat stroke and death if untreated
Low temperatures can cause hypothermia and death if untreated.
The brain monitors the body‟s temperature, if you are too hot or too cold it sends
nerve impulses to the skin.
Hairs on the skin are controlled by the erector muscle, when it contracts the hairs
stand end (goosepimples) trapping warm air near the skin, if it is too hot the erector
muscle relaxes so the hair can lie flat.
Sweating cools you down. When you are too hot, sweat is secreted onto the
surface of hot skin by glands underneath the skin. The sweat evaporates using the
heat energy from your body, which takes the heat away from the skin and cools you
down.
Blood vessels near the surface of the skin can swell (vasodilation) which cause
more blood to be passed to the surface of the skin and the heat is radiated away, or
they can get smaller (vasoconstriction) this prevents heat loss as less blood goes to
the surface of the skin so less heat gets radiated out.
Hormones
Glands in the hypothalmus
section of the brain
Thyroid
gland
Adrenal
glands
Pancreas
Ovaries
(in females)
Testes
(in males)
Gland
Ovary
Ovary
Pancreas
Testes
Hormone
Oestrogen
Progesterone
Insulin & Glucogon
Testosterone
Insulin released by
the pancreas
Target organs
Overies, uterus
Uterus
Liver
Male reproductive organs
Liver converts
Glucose to
glycogen
Glucose Increases
Glucose Decreases
Normal Blood Glucose Level
Glucose Increases
Glucose Decreases
Liver converts
Glycogen to
glucose
Glucogon released
by the pancreas
Diabetes
Diabetes is a disorder in which the blood glucose levels can be too high, there are three
main types of diabetes:
Type 1 diabetes is caused by a lack of insulin due to either a genetic disorder or as a side
effect of a viral infection.
The diabetes is controlled by
monitoring the diet
Injecting insulin
People with type 1 diabetes have to monitor their blood sugar levels throughout the day as
the level of their activity and diet changes, which will affect the amount of insulin the will
need to take in.
Type 2 diabetes is caused by a person becoming resistant to insulin due to them being very
overweight. It can be controlled by diet and exercise.
The number of people who suffer from type 2 diabetes is rising due to increasing obesity.
A person in considered obese if they have a body mass index (BMI) of over 30, if they have
a BMI of 20 or under they are considered to be underweight.
weight in kilorams (kg)
The formula for BMI is: height in metres2 (m )
2
It is important to remember that the BMI calculation is just a guide and it has many flaws,
people who have good muscle tone and who are not particularly tall may have a BMI of over
30 despite having a very healthy lifestyle.
Plant hormones
A „tropism‟ is a growth in response to a stimulus.
Auxin is a plant hormone that is made in the stem tips and roots, which controls the direction
of growth. Plant hormones are used in weedkillers, rooting powder and to control fruit
ripening.
Response
Part of plant
Direction of growth
Advantage
Positive
Stem tip
Growth towards light
To get maximum light
phototropism
for photosynthesis
Negative
Root tip
Growth away from light Less chance of drying
phototropism
out
Positive
Root tip
Towards gravity
More chance of finding
geotropism
moisture
Negative
Stem tip
Away from gravity
More chance of finding
geotropism
light.
Controlling the direction of growth
A plant grows towards the light because light destroys the auxin in that side of the stem, so
growth on that side of the plant slows down. On the shaded side the plant has more auxin,
so growth on that side speeds up. This results in the plant bending towards the light to
maximise photosynthesis.
A = The tips have been cut off removing the auxin, so phototropism can‟t happen.
B = The tinfoil caps stop the light destroying the auxin, so it remains evenly distributed and
the shoots grow straight up.
C = The light destroys the auxin on the that side of the plant, so more auxin is on the shaded
side causing the cells to elongate, so the shoot bends towards the light.