Download Example of a food chain

Learning Outcomes
What you need to
know
Unit 2
Tick off each piece of information once you have learned it.
A) ECOSYSTEMS
Habitat = The place where an organism lives (e.g. pondwater, garden
soil, mountain top, bark of tree, small village.
Population = A group of organisms of the same species (e.g. a pack of
wolves, a shoal of herring, the human inhabitants of a town, the oak
trees in a wood.
Community =The sum total of all the populations of plants, animals and
micro-organisms living together in an ecosystem. e.g. the leaves that
support the greenfly + ladybirds and small insect-eating birds.
Ecosystem = Is a natural unit made up of one or more habitats and
the communities of plants and animals living there e.g. woodland
Within an ecosystem there can be a number of different habitats each
with its own community.
Green plants are called producers because they are able to produce
their own food using light from the sun by photosynthesis.
Animals (and non-green plants like fungi) cannot produce their own food
so need to consume plants or other animals to get their energy. They
are called consumers.
A herbivore (e.g. sheep) eats plant material only.
A carnivore (e.g. tiger) eats animal material only (meat).
An omnivore (e.g. pig) eats both plant and animal material.
An animal which hunts another for food is called a predator.
The animal that is hunted is called the prey.
Decomposers are micro-organisms, such as bacteria and fungi that
obtain their energy by breaking down waste materials and dead bodies
using enzymes.
A food chain shows the relationship between organisms where one
organism feeds on the previous one.
It always begins with a green plant.
The arrow indicates the ‘direction of energy flow’.
Example of a food chain
Heather  mountain hare  eagle
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Heather is the producer
 Mountain hare is the primary consumer
 Eagle is the secondary consumer
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Many interconnecting food chains are called a food web.
E.g.
Eagle
Mountain hare
Fox
Merlin
Grouse
Skylark
Moth larva
Heather
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As energy flows through a food chain or food web energy is lost.
The energy is lost in undigested food or as heat during
movement.
Only energy used for growth can be passed on to the next
organism.
A pyramid of numbers is a diagram which represents the
number of organisms at each stage in a food chain
Tertiary consumer
e.g. pike
Secondary consumer
e.g. stickleback
Primary consumer e.g. water flea
Producer e.g. alga
•A pyramid of biomass is a diagram which represents the total
mass of organisms at each stage in a food chain.
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A pyramid of energy is a diagram which represents the
quantity of energy at each stage in a food chain.
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Biodiversity is the term used to describe the variety or
range of species present in an ecosystem.
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A species is defined as a group of organisms which can
interbreed to produce fertile offspring.
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The ecological niche of an organism is the role that it plays
within an ecosystem e.g. brown trout lives in freshwater, it is
an insect eating consumer suffering intense competition
from introduced rainbow trout
A stable ecosystem has a wide range of species and
food webs.
 An ecosystem with little variety of species is unstable
and unlikely to last.
 Few links in a chain: removing 1 animal can have a
severe effect -> unstable
 Lots of links in a chain: removing 1 animal doesn’t have
such a severe effect. -> Stable
ADAPTATIONS
 Organisms show adaptations which allow them to
successfully occupy a particular niche. Adaptations may
involve body structure and behaviour.
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An adaptation is an inherited characteristic that makes
an organism well suited to survival in its environment.
Darwin’s finches
 The main differences between the finch types are
their beaks (size and shape) and feeding habits.
 These differences allow them to exploit different
ecological niches and this will in turn increase their
chances of survival.
Desert Plants
-Long roots to absorb water deep underground
-Leaves are reduced to a spine to avoid water loss
- Some leaves have thick, waxy cuticles to further avoid water
loss.
GRAZING
 A high intensity of grazing will maintain species
diversity.
 Very high or low intensity grazing will decrease
species diversity.
POLLUTION
Pollution and habitat destruction will lead to a decrease
in species diversity.
COMPETITION
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In Plants
 Compete mainly for water, light and soil nutrients.
In Animals
 Compete for food, water and shelter.
BEHAVIOURAL ADAPTATIONS
 All animals show behavioural adaptations.
 They are often reactions by the animal to changes in its
environment.
 Such changes are called environmental stimuli e.g.
light, humidity
 The animal’s reaction is called a behavioural response.
Woodlice and humidity
 When woodlice enter a dry environment their rate of
movement increases.
 When they enter a damp area they slow down again.
 This response to humidity ensures that woodlice remain
mainly in a moist/humid environment and are less likely
to die from drying out.
Woodlice and light
 When given the choice in a choice chamber, woodlice
will move to the dark side. By staying in dark places,
this behaviour will increase their chance of survival.
Factors affecting Variation in a species
Continuous variation
 A characteristic shows continuous variation when it
varies in a smooth continuous way from one extreme to
the other and does not fall into naturally distinct
groups. e.g. height, weight, eye colour, hand span in
humans, tail length in mice, body length in salmon.
Discontinuous variation
 A characteristic shows discontinuous variation if it can
be used to divide up the members of a species into 2 or
more distinct groups e.g. human blood group, tongueroller/non-roller, human fingerprint type.
FERTILISATION
Mammals
 Mammalian gametes (sex cells) are eggs and sperm.
 Eggs are produced in the ovaries.
 Sperm are produced in the testes.
 Sperm and eggs both contain a nucleus.
 Fertilisation is when these 2 nuclei fuse together to form
a zygote (a fertilised egg cell).
 Variation within the zygote is produced by a random
combination of parental gametes.
Flowering plants
 The sex cells or gametes in flowering plants are found in:pollen and ovules.
 Pollen is produced by the anther. Pollen contains the male
gamete.
 Ovules are produced by the ovary which contains the
female gamete.
 A pollen grain lands and becomes attached to the stigma.
The pollen grain bursts open and then starts to grow a
pollen tube which grows towards the ovule.
•
The nucleus of the male sex cell in the pollen fuses with
the nucleus of the female sex cell in the ovule.
 This is called fertilisation.
 When the male and female nuclei fuse together a zygote is
formed which contains the genetic information of both
parent plants.
GENETICS
 Chromosomes contain genetic information that gives rise
to an organisms’ characteristics.
 Chromosomes are described in terms of a chain of DNA
bases.
 The order of the DNA bases encodes information for the
sequence of amino acids in proteins.
 These in turn dictate the structures and therefore
functions of these proteins.
e.g. the protein haemoglobin gives red blood cells their
characteristic colour.
DIVISION OF THE NUCLEUS IN GAMETE PRODUCTION
 Gametes have 1 set of chromosomes.
 Body cells have 2 matching sets of chromosomes.
 The reduction in number of chromosomes to a single set
occurs during gamete formation (meiosis)
 The 2 sets of chromosomes are restored at
fertilisation.
 Matching chromosomes pair and then separate during
meiosis.
 The random assortment of chromosomes during meiosis
leads to variation in offspring.
CHROMOSOME NUMBERS IN DIFFERENT SPECIES
 Humans have 23 chromosomes in one set giving a total of
46 chromosomes in a normal body cell.
 Different species have different numbers of
chromosomes (chromosome complement).
SEX DETERMINATION
 In humans, each male gamete has an X or a Y
chromosome.
 Each female gamete has an X chromosome.
 Female = XX Male = XY
CHARACTERSITCS CONTROLLED BY FORMS OF A GENE
CALLED ALLELES
 Genes are part of chromosomes.
 Different forms of a gene are called alleles.
 Each gamete carries 1 allele of the gene.
 HOMOZYGOUS = An individual with 2 of the same allele
e.g. TT or tt.
 HETEROZYGOUS = An individual with 2 different alleles
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of a gene, e.g Tt
The genetic symbols an individual has is its GENOTYPE,
e.g. Tt
The physical appearance an individual has is its
PHENOTYPE e.g. Tall
If a tall plant and a dwarf plant cross, the offspring are
all tall. This means that ‘Tall’ is dominant. ‘Dwarf’ is
recessive.
The dominant form of the gene always gets a capital
letter e.g. T = tall.
The recessive form of the gene always gets the same
letter but lower case e.g. t = dwarf
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TRUE BREEDING
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When 2 lilac parent plants cross, the offspring are all
lilac. When the lilac offspring cross, all their offspring
are lilac. SO: - When the flower colour of the offspring
is identical to the parent flower colour, the members of
the strain are true breeding. (they are always
homozygous, e.g. LL)
MONHYBRID CROSSES
 P = parent
 F1 = 1st filial generation
 F2 = 2nd filial generation
 A monohybrid cross is a cross that involves only one
difference between the original parents, e.g. flower
colour or height.
 Parents in monohybrid crosses are usually true breeding
and show different phenotypes.
 You should be able to solve monohybrid cross problems
following from the P generation to the F2 generation
using dominant and recessive alleles.
PRORTIONS AND RATIOS OF PHENOTYPES OF THE
F1 and F2 OFFSPRING
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The predicted ratio of F2 offspring is 3:1 from a cross
between 2 true breeding parents e.g. Pea plants
P
Tall
TT
F1
X
Dwarf
tt
Tt
F2…….Cross Tt with Tt
Gametes
T t and T t
T
t
Genotypic ratio:
Phenotypic ratio:
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T
TT
Tt
t
Tt
tt
1TT: 2Tt: 1tt
3Tall : 1 dwarf
A 3:1 ratio rarely happens in nature since and the
observed ratio is not always as predicted since
fertilisation is a random process involving an element of
chance.
CO-DOMINANCE
2 alleles of a gene can be co-dominant when neither is
dominant nor recessive. Both alleles are displayed in the
phenotype.
Example: Black stallion crossed with White mare
BB
X
WW
F1
BW
Grey roan (mix of black and white hair).
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You should be able to solve co-dominance problems.
POLYGENIC INHERITANCE
A range of phenotypes is produced e.g. skin colour in
humans, seed mass in plants. The characteristics arise
due to the interaction of the alleles of several genes.
ENVIRONMENTAL IMPACT ON PHENOTYPE
 The final appearance of an organism (phenotype) is the
result of its genotype and the effects of the
environment.
 If organisms of identical genotype are subject to
different environmental conditions they show
considerable variation.
 Such changes have little evolutionary significance as
they are not passed from one generation to the next.
NATURAL SELECTION
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Is the process by which organisms that are better
adapted to their environment survive and breed,
while those less well adapted fail to do so.
The better adapted organisms are more likely to pass
their characteristics to succeeding generations. E.g.
peppered moth.
SELECTIVE BREEDING
The selective breeding of plants and animals showing
desirable characteristics.
 Over several generations improved offspring may
result.
 Takes a relatively long period of time and the results
are not always guaranteed.
GENETIC ENGINEERING
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The stages in the production of a desired product
need to be known e.g. insulin, HGH.
THE STAGES
 Identification and removal of required gene from
source chromosome
 Insertion of required gene into bacterial plasmid
 Insertion of plasmid into bacterial cell
 Synthesis of required product by bacteria.
Advantages of genetic engineering
 increased range of products and increased rate of
production.
Disadvantages of genetic engineering
 possible release of genetically engineered
bacteria into the environment and costly to
develop.
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