Download N5 Multicellular Organisms Course Notes

Multicellular Organisms
Calderglen High School
National 5 Biology Unit 2
Multicellular Organisms
1
Multicellular Organisms
Sub topic: Producing new cells
Chromosomes are found in the nucleus of the cell and carry coded instructions called genes
from one generation of cell to the next. When most plant and animal cells divide, their nuclei
pass through the same series of changes, called mitosis.
A cell
chromosomes
nucleus
chromatid
centromere
A chromosome
Image BBC Bitesize
Keeping the chromosome number correct
Each species of plant and animal has a characteristic number of chromosomes in the nucleus of
each of its body cells which is always the same for the specific species.
For example, the body cells of human beings contain 46 chromosomes.
Mitosis provides new cells for growth and repair of damaged cells and maintains the diploid
chromosome complement.
2
Multicellular Organisms
Summary of the stages of mitosis
The diagram below represents stages in the process of mitosis in the correct sequence.
After a period of growth,
mitosis starts again each
cell
Two identical
daughter cells
have been
produced.
Spindle fibres pull
chromatids to opposite
ends of the cell.
Chromosomes become
visible in the nucleus.
Chromosomes
shorten and appear
as chromatids joined
at the centromere
Nuclear membrane
disappears and the
chromosomes line
up along the
equator of the cell.
3
Multicellular Organisms
Stem Cells
Stem cells in animals are unspecialised cells that are involved in growth and repair.
They are able to:


reproduce themselves by repeated mitosis while remaining unspecialised.
develop into various types of specialised cells when required e.g. red blood cell, nerve
cell or bone cell.
Liver
Bone
Image BBC
Bitesize
Nerve
Red blood cell
Possible uses of stem cells include the treatment of diabetes and cancer, repair to body organs
including bone and the windpipe or even the growth of organs for transplant such as liver and
skin.
Cell organisation
Specialisation of cells leads to the formation of a variety of cells, tissues and organs. Groups of
organs which work together form systems.
The cells are organised in the hierarchy as shown below
Cells
Tissues
Eg
muscle
and
bone.
Organs
Eg liver,
eye or
stomach
Systems
Eg
circulatory
system,
digestive
system
Organisms
4
Multicellular Organisms
Sub topic: Control and Communication
In a multicellular organism, cells communicate using nerve impulses or hormones.
Nervous control
The brain and spinal cord are made of neurons. The brain and the spinal cord make up the
central nervous system (CNS).
Many nerves join with the CNS. They bring messages as nerve impulses from sensory organs
which contain cells called receptors.
The CNS sorts this information and processes it.
To trigger a response, a different group of nerves are used to carry messages from the CNS to
effectors which are usually muscles.
image bbc bitesize
5
Multicellular Organisms
The Brain
The brain plays a very important part in the way you respond to any factors that may affect
your body. Just to read this page, millions of nerve messages are zipping around within your
own brain.
The brain itself is made up of several different parts or regions, each with its own specialised
function.
image bbc bitesize
Part of the brain
Function
Cerebrum
Controls conscious actions, as well as
reasoning and learning.
Cerebellum
Balance and muscle co-ordination
Medulla
Controls the rate of breathing and
heartbeat.
6
Multicellular Organisms
Neural pathways
This involves three types of neurons. Neurons are highly specialised because they carry
electrical impulses, they do not come in contact with one another:
 A sensory neuron which carries electrical impulses from a sense organ to the CNS.
 A relay neuron which is located in the brain or spinal cord. It receives electrical impulses
from the sensory neuron and transmits them to other neurons involved in the response.
 A motor neuron which receives electrical impulses from relay neurons and transmits them to
a muscle or gland which will carry out the response.
When stimulated by an electrical impulse, muscles respond by contract and glands by
releasing chemicals. Muscle responds more rapidly than glands.
 Reflex actions are fast responses that do not normally involve conscious thought. They
usually protect your body from harm. Examples of reflex actions include sneezing when
foreign particles enter the nose, withdrawal of a hand from a hot object, blinking when an
object moves near the eye.
 The circuit of the neurons that act to produce the reflex action is called the reflex arc (refer
to the diagram on the next page)
Image from BBC Bitesize
Relay neuron
Sensory neuron
Motor neuron
Reflex arc
muscle
Burning candle
7
Multicellular Organisms
 The transmission of a nerve impulse through a reflex arc is called a reflex action. In the
example above the sensory neuron in the hand detects the heat and this initiates an
electrical impulse which travels towards the relay nerve. The impulse is transferred to the
rely nerve which passes on the impulse to the motor nerve. The nerve impulse travels along
the motor nerve to the muscle which brings about a muscle contraction and the hand is
withdrawn from the heat.
 The neurons do not touch, there is a small gap called a synapse between neurons which
allows chemicals to transfer from one neuron to another.
Sensory neuron
Relay neuron
Motor neuron
Synapse (gap
Synapse (gap
between neurons)
between neurons)
Hormonal control
Hormones are made up of proteins. They are chemical messengers which pass on information to
target tissues which have special receptor cells sensitive to that specific hormone. Only some
tissues are affected by specific hormones. Glands which release hormones into the bloodstream
are known as endocrine glands.
Endocrine system
Image from BBC Bitesize
Pancreas
Testes
(male)
Ovary
8
Multicellular Organisms
Regulation of Blood Glucose Level in the Blood
Cells are constantly using up glucose present in
the bloodstream for energy.
A rise in blood glucose concentration is detected
by cells in the pancreas. These cells produce the
hormone insulin. This hormone is transported in
the blood to the liver where it activates glucose
to be converted to glycogen. This brings blood
glucose concentration down to around its normal
level.
Scran image
If the blood glucose concentration drops a different set of cells in the
pancreas detect this change and release the hormone glucagon into the
bloodstream. This second hormone is transported to the liver and activates the
conversion of glycogen to glucose. The blood glucose concentration therefore
rises to its normal level.
Regulation of Blood Glucose levels
Insulin produced when blood glucose level
is above the normal level
blood glucose level
Glycogen in the
liver
Glucagon is produced when the blood
glucose level falls below the normal level
9
Multicellular Organisms
Sub topic: Reproduction
Diploid Cells







After fertilisation, a zygote (fertilised egg) is formed.
The cell is DIPLOID
A diploid cell has 2 sets of chromosomes (in humans this is 46 chromosomes).
One set has come from the male parent and one set has come from the female parent.
Every body cell has a copy of the chromosomes that was in the zygote.
Therefore, every body cell is a diploid cell.
The diploid number in humans is 46.
Haploid Cells






Eventually, the adult will produce sex cells.
Another name for the sex cells is GAMETE.
Gametes will only have one set of chromosomes.
A HAPLOID cell has only one set of chromosomes
The haploid number in humans is 23.
Fertilisation
Fertilisation is the fusion of the nuclei of the two haploid gametes to produce a diploid
zygote, which divides to form an embryo.
Haploid
Haploid
Gamete eg
Gamete eg
egg
sperm
Fertilisation
produces a
diploid
zygote
10
Multicellular Organisms





Gamete Production in Animals
Like plants, animals produce gametes in sex organs.
In human males, SPERM are produced in the TESTES.
In human females, EGGS (ova) are produced in the OVARIES.
Millions of sperm cells are produced in the testes and are able to swim in fluid using their
long tails.
Egg cells are the largest human cells because of the large food store in the cytoplasm.
Sperm (male gamete)
Egg (female gamete)
head
tail
Cell membrane
nucleus
Cytoplasm
containing a
food store
Scran
images
11
Multicellular Organisms
Animal Reproductive System
Male reproductive system image bbc bite size
sperm duct
penis
Testes
Female reproductive system image bbc bitesize
testes
ovary
womb
Sexual Reproduction in Plants






Flowers are the organs of sexual reproduction in plants.
The flower contains both the male and female parts.
The ANTHER and FILAMENT together is known as the STAMEN. This is the male parts of
the flower.
The male anther is the site of gamete production. The diploid anther cells produce the
haploid pollen grains, which contain the male gametes.
The OVARY is the female part of the flower.
The female ovary is the site of gamete production. The diploid ovary cells produce
haploid eggs (the female sex cell or gamete).
12
Multicellular Organisms
Sub topic: Variation and Inheritance



A characteristic shows DISCRETE VARIATION if it can be used to divide up the members
of a species into two or more distinct groups.
Humans can be split up into two groups depending on their ability to roll their tongue and
into four groups based on blood group types A, B, AB and O.
Data obtained from a survey of a characteristic that shows discrete variation is
represented by a bar chart
Discrete variation
graph
Image bbc
bitesize

Some characteristics are controlled by the alleles of a single gene – they are expressed as
clear-cut PHENOTYPIC groups showing discrete variation.

In humans, the ability to roll the tongue is an example of the single gene inheritance.

In pea plants, the possession of lilac or white flowers is an example of single gene
inheritance.
13
Multicellular Organisms
Continuous Variation

A characteristic shows continuous variation when it varies amongst the members of a
species in a smooth, continuous way from one extreme to another and does not fall into
distinct groups.

CONTINUOUS VARIATION can be represented by a normal DISTRIBUTION CURVE (the
curve would be bell shaped).
Image bbc bitesize





Few individuals show values close to the extremes of the range.
Most individuals show values close to the middle of the range (also known as the
average).
Some characteristics are controlled by the alleles of several genes.
This results in the characteristic being expressed as a range of PHENOTYPES e.g. Human
height.
A characteristic showing CONTINUOUS VARIATION controlled in this way by more than one
gene is said to show polygenic inheritance.
Phenotypes and Dominant Genes










For every characteristic we have 2 genes – one from our mother and one from our father.
Genes are part of chromosomes.
Each characteristic is controlled by two forms of a gene.
Each parent contributes one form of the gene.
Each gamete (sex cell) carriers one of the two forms of the gene.
Differing forms of a gene are called ALLELES.
Example – The alleles for the gene for eye colour are blue, brown, green, etc.
PHENOTYPE – this is the physical appearance resulting from the inherited information.
Example – Someone with blue eyes has the phenotype blue eyes.
Genes or alleles can be said to be DOMINANT (shows up in the phenotype) or RECESSIVE
(hidden when it is present along with the dominant gene).
14
Multicellular Organisms


GENOTYPE – this is the combination of genes in a gene pair.
Genotype is represented by 2 letters (one letter for each gene).
Note – the phenotype of this
individual is Black Hair
Dominant
black gene






Recessive
white gene
If the 2 alleles that an organism possesses for a characteristic are identical, the organism
is said to be HOMOZYGOUS for the characteristic.
BB has a phenotype black it is said to have a HOMOZYGOUS genotype.
Homozygous is often called ‘pure breed’ or ‘true breeding’.
Bb has the phenotype black but it is said to have a HETEROZYGOUS genotype.
If the 2 alleles that an organism possesses for a characteristic are different, the organism
is said to be HETEROZYGOUS for that characteristic.
bb has the phenotype white and is said to be HOMOZYGOUS recessive.
15
Multicellular Organisms
Genetic Crosses
A genetic cross is laid out as follows:
 A pea plant which produces round pea seeds is crossed with a pea plant which produces
wrinkled pea seeds.
 All the offspring are round.
R:
Round
r:
Wrinkled
Parents Phenotype (P)
Round
Parents Genotype (P)
X
RR
Gametes
Wrinkled
X
R
rr
X
First Generation (F1) Genotype
Rr
First Generation (F1) Phenotype
Round
F1 X F1 =
Rr
Gametes
Genotype
X
R,r
RR
Rr
Rr
r
Rr
R, r
rr
Second Generation (F2)
Phenotype
Round
Round
Round
Wrinkled
Second Generation (F2)
F2 Phenotypic ratio
3
:
1
The actual ratio may differ from the expected ratio since fertilisation is a random process. An
element of chance is involved.
16
Multicellular Organisms
Sub topic: Transport systems in Plants
Plant organs are roots, stems and leaves.
Transport of water in plants
Root Hair Cell
Image BBC Bitesize
The root hair is an extension of the root cell and water is taken in by osmosis through the cells
selectively permeable membrane. When this cell has taken on a reasonable amount of water it
will have a higher water concentration than the next cell and so water will pass to this next cell
by osmosis. This process continues until the water reaches specialised water transport vessels
called xylem.
Image – BBC Bitesize
Root
epidermal
Xylem
cell
vessel
Water travels across the root cortex cells by
osmosis and then enters the xylem vessels.
17
Multicellular Organisms
Xylem
Water and minerals are transported from
the roots upwards to the leaves. Xylem
forms when the nucleus and end walls of
Rings of lignin
the cells disintegrate forming long hollow
(give plant
lignified tubes. Xylem is a non-living
support)
material.
Image – BBC Bitesize
Water movement in xylem vessels
Transpiration is the evaporation of water from the mesophyll cells in the leaves of plants. Water
evaporates through stomata whose opening and closing is controlled by guard cells, which are found
in the leaf epidermis (outer layer of cells). In order to replace this lost water, water is pulled up
through the xylem vessels. Mesophyll cells in the leaf require water for photosynthesis and this is
delivered via the xylem vessels.
Section of leaf
Mesophyll
cell in the
leaf
Air space in
Xylem
leaf
Lower
epidermis
Stoma
Guard cell
Image – BBC Bitesize
18
Multicellular Organisms
Factors affecting transpiration
The following factors affect the rate of transpiration; temperature, humidity, air movement and
light. These factors are known as abiotic factors.
Factor affecting
Transpiration rate
transpiration rate
Temperature
Surface area of leaf
An increase in any of these factors will result in an
increase in the rate of transpiration
Wind speed
Humidity
An increase humidity will result in decrease in
the rate of transpiration
Opening and closing of stomata
When the guard cells become turgid this forces the stoma open. When the guard cells are
flaccid the stoma closes.
guard
cells
stoma
epidermis
Stoma open
Stoma closed
Images – BBC Bitesize
19
Multicellular Organisms
Diagram of a leaf showing the position of the stoma.
Image BBC Bitesize
stoma
Transport of sugar in plants
Sugar is transported up and down the plant in living phloem cells.
Sieve plate
Image -BBC Bitesize
Companion cell
Sieve cell
Differences between Xylem and phloem
Xylem
Phloem
Transports water and minerals
dead
lignified
No companion cell
No sieve plates
Transports sugar
living
Not lignified
Companion cell
Sieve plates
20
Multicellular Organisms
Sub topic: Transport Systems in Animals
The role of blood
Blood consists of blood cells and the fluid
that surrounds them called plasma.
Many substances are transported
dissolved in plasma including glucose and
amino acids.
Blood consist of two parts
Plasma
Other blood cells
Red blood cells
White blood cells are part of the immune system and are involved in destroying pathogens
(disease causing micro organisms). There are two main types of cells involved:
 Phagocytes carry out phagocytosis by engulfing pathogens
 Lymphocytes which produce antibodies which destroy pathogens. Each antibody is
specific to a particular pathogen.
Red blood cells transport oxygen from the lungs to body cells. The pigment haemoglobin found
in the red cells reacts with oxygen at the lungs to form oxyhaemoglobin. At the tissues the
oxygen is released to diffuse into the cells.
Red blood cells have no nucleus In order to
maximise the space available to carry
oxygen. They are very small to fit through
the smallest blood vessels and have a
biconcave shape that increases their
surface area.
Image source
SCRAN
Red blood cells
In mammals the main transport system is the circulatory system, comprising of the heart and
associated blood vessels. The heart is a muscular pump, pumping blood around the body to
deliver nutrients and oxygen as well as dispose of carbon dioxide and waste. The wall of the left
ventricle is thicker than that of the right because it has to pump blood all round the body.
21
Multicellular Organisms
Structure of the heart
Valve at exit to
pulmonary artery
Valve at exit to
aorta
Right atrium
Left atrium
Right ventricle
Left ventricle
Image from BBC Bitesize
Valves between atria
and ventricles
Valves in the heart and in veins prevent the backflow of blood
22
Multicellular Organisms
Circulation
Pulmonary
vein
aorta
Pulmonary
artery
Image from BBC Bitesize
Vena cava
Deoxygenated blood
Oxygenated blood
The Coronary artery
The first branch of the aorta
leaving the heart is the coronary
artery and this supplies the heart
muscle with oxygenated blood.
The diagram on the right also
shows how a build up of lipid
material called plaques can lead to
a coronary heart attack.
A heart
Coronary
artery
23
Multicellular Organisms
Blood Vessels
Arteries carry blood away from the heart. They have a thick muscular wall and a narrow central
channel. The blood in arteries is under high pressure.
Veins carry blood towards the heart they have a thinner muscular wall than arteries and a wider
central channel. The blood in veins is under low pressure and they contain valves to prevent
backflow of blood.
Artery
Vein
Valve
Wide cental channel
narrow
central
Thick muscular wall
Thin muscular
wall
channel
Capillary
Capillary
Thin central
channel
Capillaries are exchange vessels. Their
walls are only one cell thick to allow
materials to cross from tissues to
capillaries easily. There is a dense
network of capillaries giving a large
surface area. Examples of materials that
cross capillary walls are oxygen and
glucose into cells and carbon dioxide and
urea from cells to the capillary.
24
Multicellular Organisms
Sub topic: Absorption of materials
Oxygen and nutrients from food must be absorbed into the bloodstream to be delivered to cells
for respiration. Waste materials such as carbon dioxide must be removed from cells into the
bloodstream to be removed from the body.
Tissues contain capillary networks to allow the exchange of materials at a cellular level.
Surfaces involved in the absorption of materials have certain features in common, these
include:
 A large surface area
 Thin walls
 Extensive blood supply
All these features increase the efficiency of absorption.
Function of the lungs
At the lungs gas exchange takes place. Carbon dioxide diffuses from capillaries into the alveoli
and oxygen diffuses from the alveoli into the capillaries.
The Lungs
lung
airways inside the
lungs
alveoli
25
Multicellular Organisms
Deoxygenated
blood
Air in
Air out
Oxygenated
blood
Alveolus and the large capillary network
An alveolus showing gas exchange Image from scran
deoxygenated blood
oxygenated blood
O2
CO2
Red blood cell
26
Multicellular Organisms
Feature of a gas exchange surface
Feature
large surface area
thin lining
surrounded by large capillary
network
Function
to absorb oxygen
eases diffusion of oxygen into blood
to pick up and transport oxygen
Digestive System
small intestine
Image from SCRAN
Image BBC Bitesize
The small intestine’s internal surface is folded and has thousands of finger like projections
called villi. The large number of thin walled villi provides a large surface area. Each villus
contains a network of capillaries to absorb glucose and amino acids and a lacteal to absorb fatty
acids and glycerol.
27
Multicellular Organisms
Structure of a villus
Thin wall of the villus
Blood capillary absorbs
glucose and amino
acids
Lacteal –
Absorbs fatty acids and
glycerol
Image Scran
Image from
SCRAN
28