Download CORE SCIENCE B1 Topic 1 revision

Topic 1 – Classification,
Variation and Inheritance
How are organisms classified?
• Kingdom (Animalia, Plantae, Fungi, Prokaryotae
(bacteria), Protoctista)
• Phylum
• Class
• Order
• Family – always ends ‘ae’ or ‘ea’
• Genus – Italicised, capital letter
• Species – Italicised, lower case letter,
How to remember the order
Linnaeus
Classification
Kingdom
Phylum
Class
Order
Family
Genus
species
Mnemonic
Largest
Smallest
Knowledge
Plus
Careful
Observation
Frequently
Guarantees
success
Binomial classification
An American Robin
Turdus migratorious
A British Robin
Erithacus rubecula
These birds both have the common name ROBIN but they are
not from the same species, how do we know?
The 5 Kingdoms
• Vertebrates = having a backbone
or spinal column. (eg cat, human,
fish, frog) phylum chordata.
• Invertebrates = Lacking a
backbone or spinal column. (eg slug,
starfish, insects)
The 5 Classes of Vertebrates
Name
Main characteristics
Fish
Have wet scales and gills, lay
eggs in water.
Amphibians
Have smooth, moist, permeable
skin. Adults have lungs. They
lay eggs in water.
Reptiles
Have dry, scaly skin. Have lungs
They lay leathery shelled eggs.
Mammals
Have hair on their body and
mammary glands that produce
milk. Have lungs. They give
birth to live young.
Birds
Have feathers and a beak.
Have lungs. They lay hard
shelled eggs.
Classifying vertebrates
Absorbing oxygen?
• Fish and young amphibians = gills
• Mammals, birds, reptiles and adult amphibians = lungs
Reproduction?
• Internal fertilisation – sperm meets egg inside the body = mammals
• External fertilisation – female lays eggs then male releases sperm onto
them = fish, amphibians
Maintaining Body temperature?
• Homeotherms – keep body temperature constant by releasing heat to
their surroundings = mammals
• Poikilotherms – body temperature changes with surroundings = reptiles
Species
Species are organisms that are capable of
interbreeding to produce fertile offspring.
Have Binomial Names eg Homo sapiens
Exceptions
Felis catus
1. Hybrids (cross between 2 different species)
eg horse and donkey = mule
2. Ring Species Sometimes there are a chain of
neighbours that can all breed with their
neighbour but the ones at either end can’t.
These are called a ring species.
Variation
Differences within a species.
• Environmental – Caused by the environment eg. hair
length, sun tan
• Genetic – inherited eg. natural hair colour, eye colour,
certain diseases such as cystic fibrosis
• Continuous variation – range from low to high eg height,
weight
• Discontinuous variation – distinct categories eg eye
colour
Normal Distribution (Bell Shaped) Curve
Height
Natural Selection
Cells and DNA
Alleles
• An allele is an
alternative form of a
gene (one member of a
pair).
• Organisms have two
alleles for each
characteristic eg hair
colour, eye colour.
Sexual Reproduction in humans
Gamete
(egg)
23
chromosomes
23
chromosomes
Gamete
(Sperm)
23 pairs of
chromosomes
(one from each
gamete)
Normal
Body Cell
Punnet squares
• Capital letters show
dominant alleles
• Lower case letters show
recessive alleles
• The letters in the boxes
represent the genotype
• The characteristic you see
is called the phenotype e.g
red flowers
Complete the punnet square and predict the
phenotypes of the next generation.
•The dominant allele for
brown eyes is B.
•The recessive allele for
blue eyes is b.
A mother with brown eyes
and a genotype Bb
reproduces with a father
with brown eyes and
genotype Bb.
What chance does the next
generation have of having:
Brown eyes?
Blue eyes?
BB or bb = homozygous
Bb = heterozygous (carriers are hetero)
B
b
B
BB
(brown)
Bb
(Brown)
b
Bb
(Brown)
bb
(blue)
Ratio =
3 brown:1 blue
Probability =
3 in 4 brown
1 in 4 blue
Percentage chance =
75% brown
25% blue
Cystic Fibrosis
Inherited disease caused by 2 recessive alleles (cc).
Dominant allele (C) causes person to be CC – healthy
or Cc - carrier.
Symptoms
thick sticky mucus on lungs
coughing
bacterial chest infections
Breathlessness
What chance of having cystic fibrosis from two
carrier (Cc) parents?
Cystic Fibrosis
1a. Which people
have the
disease?
b. What alleles do
they have?
Dominant – C
Recessive - c
2. Al and Bev have
the same alleles –
what are they?
Al
Izzie
Bev
Jack Deb
Fred
Helen
Gary
Emma
3a. Izzie could
have 2
combinations of
alleles – what
could they be.
b. Why can we
not tell from this
diagram which
ones they are?
Sickle Cell Anaemia
Inherited disease caused by two recessive
alleles (ss). Healthy = SS Carrier = Ss
Red blood cells become mis shaped so can’t
carry as much oxygen.
Symptoms
•Tiredness
•Shortness of breath
•Pale skin
•Fainting