Transcript Unit 2 Multicellular Organisms Mr Gravell

National 5 Biology Course Notes
Unit 2 : Multicellular Organisms
Part 1 :
Cells, tissues and organs
Tissues
Tissues are groups of cells that have the same structure and function.
Each tissue consists of similar specialised cells.
Organs
An organ is made up of different types of tissue
e.g. the heart
The heart is an organ that pumps blood around the body
It is composed of several tissues, e.g.
Muscle
Nervous tissue
Blood
e.g. ciliated epithelium in the windpipe –
specialised to sweep dust out of the windpipe
A plant organ – the leaf
A leaf is an organ whose function is photosynthesis.
The diagram shows the layers of cells found inside the leaf
Leaf tissues
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis
The leaf also contains two transport
tissues xylem(transports water)
and phloem (transports sugar) in
the leaf veins
Summary of organisation of cells in multicellular organisms
Are grouped together in
CELLS
TISSUES
Several different
tissues are found in an
ORGAN
Groups of similar cells
with the same
function
Organs with similar
functions are
grouped into
ORGAN SYSTEMS
For example, the digestive
system, the nervous system
National 5 Biology Course Notes
Unit 2 : Multicellular Organisms
Part 2 :
Cells, tissues and organs
Stem cells
Stem cells are found in animals.
They can
1. Divide by mitosis to provide more stem cells
2. Differentiate (develop into specialised cells).
Types of stem cells
Two types depending on where they are found
1. Embryonic stem cells
These are found in embryos
They can develop into any type of body cell
They produce cells for growth of the embryo
2. Adult (tissue) stem cells
Found in fully formed animals (babies and children as well as adults)
They can develop into a limited range of cell types, e.g. stem cells found in bone marrow can only become blood cells
They produce cells for repair of the body
Potential uses of stem cells and ethical issues
Stem cells have current and potential medical uses.
Since embryonic stem cells can become any type of cells, they are potentially the most useful but there are
ethical issues involved in their use since the embryos are destroyed to get the cells.
Meristems
Meristems are areas of plants that contain cells that divide by mitosis to produce new cells for growth of the
plant.
In plants cells that divide are found only at meristems and the unspecialised cells produced can become any type
of plant cell.
Meristems are found
• At the root and shoot tip – these produce new cells for increase in length of the root and shoot
• Between the xylem and phloem – these meristems produce new cells for increase in thickness of the root and
shoot
Meristems at
the shoot and
root tips
provide new
cells for growth
in the length of
the root and
shoot
Meristem between the xylem
and phloem provides new cells
for growth in thickness of the
root and shoot
National 5 Biology Course Notes
Unit 2 : Multicellular Organisms
Part 3 : Control and communication
Nervous control
Central nervous system
(brain and spinal cord)
The nervous system
The nervous system consists of:
• The central nervous system (CNS) – the brain and spinal cord
• The peripheral nervous system – all the other nerves
Peripheral
nervous
system
Structure and function of the brain
Part of the brain
cerebrum
cerebellum
medulla
Function
cerebrum
Thoughts, memories, reasoning,
receives messages from sense organs,
conscious muscle control
cerebellum
Controls balance
medulla
Control of involuntary actions,
e.g. heartbeat, breathing rate
Neurons
Neurons are nerve cells.
There are three kinds of neurons:
Sensory neurons
These carry nerve impulses from sense
organs to the central nervous system
Motor neurons
These carry nerve impulses from the
central nervous system to muscles and
glands
Relay neurons
Found in the central nervous
system. Carry nerve impulses
from sensory neurons to motor
neurons.
Reflex actions
Reflex actions are
• fast
• inborn – don’t have to be learned
• carried out in the same way be all members of the species
• for protection
Examples of reflex action
• Pupil size decreasing in bright light
• Sneezing when dust enters the nose
• Pulling hand away from a very hot object
Reflex arc
A reflex arc is the path followed by a nerve impulse when carrying out a reflex action.
A stimulus is detected by a
receptor, e.g. receptors in
the skin detect a hot object
A nerve impulse passes along
a sensory neurone to the
central nervous system
A nerve impulse passes along
a relay neurone in the
central nervous system
The effector responds (e.g.
the muscle contracts and
pulls the hand away from the
hot object)
A nerve impulse passes along
a motor neurone to a muscle
Effectors
Sensory cells in
skin
Sensory
neurone
synapse
Spinal
cord
Relay neurone
muscle
Motor
neurone
Effectors can either be muscles bringing
about a fast response, for example when
the hand is pulled away from a hot
object or glands bringing about a slow
response, e.g. sweat glands producing
sweat when the temperature increases.
Synapse
Where two nerve cells meet, there is a microscopic space between them called a synapse.
When a nerve impulse reaches the end of the first neurone, it causes release of a chemical that triggers a nerve
impulse in the second neurone.
End of first neurone
Synapse
Start of second neurone
Nerve impulse reaches
the end of the first
neurone
This causes release of a chemical
that diffuses across the synapse
And triggers a nerve impulse
in the second neurone
Hormones
As well as the nervous system, parts of the body can communicate through hormones.
Hormones are chemical messengers produced by endocrine glands.
The endocrine glands release their hormones directly into the blood as it flows through the gland.
Hormones travel around the body in the blood but they have an effect only in certain parts called the target tissues of the
hormone.
This is because the target tissues have receptors on their cells that the hormone can bind to.
Control of blood glucose
Blood glucose is controlled by two hormones produced in the pancreas called insulin and glucagon.
Blood glucose
increases after
eating
Blood glucose
decreases
after fasting
Pancreas
releases
insulin into
the blood
Pancreas
releases
glucagon into
the blood
Insulin
reaches the
liver
Glucagon
reaches the
liver
Liver changes
glucose in the
blood to
glycogen and
stores it
Blood glucose
level
decreases
back to
normal
Liver changes
stored glycogen
into glucose
Blood glucose
level increases
back to
normal
Diabetes
Diabetes results either from the body producing no insulin or too little insulin (type 1 diabetes) or from body cells
not responding to insulin (type 2 diabetes).
Type 1 diabetes is treated by insulin injections while type 2 may be treated by lifestyle changes, e.g. healthy diet and
exercise.
Untreated diabetes can result in damage to small blood vessels especially of the eyes and kidneys resulting in
blindness and/or kidney failure.
National 5 Biology Course Notes
Unit 2 : Multicellular Organisms
Part 4 : Reproduction
Reproduction
Body cells are diploid.
The fertilisation of haploid gametes to produce a diploid zygote.
Body cells have 2 sets of chromosomes (one set comes from each parent) – these cells are diploid.
Sex cells are called gametes, they have one set of chromosomes and are said to be haploid.
Fertilisation
Fertilisation occurs when a male and a female gamete fuse.
The cell produced by fusion of gametes is called a zygote.
The zygote is diploid
Haploid
male and
female
gamete
fertilisation
Diploid zygote
The structures and sites of gamete production in plants and animals
Flowering plants
The diagram shows structures in a flower
Pollen grains, which contain the male gamete, are
produced in the anther
anther
ovules
ovary
Ovules, which contain the female gamete are produced in the ovary
Mammals
Male gametes (sperm
cells) are produced in
the testes
Female gametes
(eggs) are
produced in the
ovaries
testis
ovary
Comparison of discrete and continuous variation
Most features of an individual phenotype are polygenic and show continuous variation.
Identification of phenotype and genotype, dominant and recessive characteristics and
homozygous and heterozygous individuals.
Comparison of discrete and continuous variation
Discrete variation
Characteristics that show discrete variation are those that have clear cut differences which allow a member
of a species to be put into a particular distinct group.
Examples of characteristics in humans that show discrete variation are:
Gender
Right or left handed
Tongue roller or non-roller
Attached or unattached ear lobes
Continuous variation
These characteristics show slight differences between individuals between an extreme upper and lower value
Examples of characteristics in humans showing continuous variation are
Height
Body mass
Hand span
Foot length
What type of variation is shown by these characteristics
Round or wrinkled seed in pea plants
Discrete variation
Milk yield in cattle
Continuous variation
Blood group in humans
Discrete variation
Resting heart rate in humans
Continuous variation
Identification of phenotype and genotype, dominant and recessive characteristics and homozygous and
heterozygous individuals.
Phenotype
The characteristics an organism has / its appearance
Genotype
The genes that an organism has for a characteristic
Alleles
Different forms of a gene / different genes for the same characteristic, e.g. the gene for blue eyes
and the gene for brown eyes are alleles
Homozygous
Having two identical genes for a characteristic
Heterozygous
Having two different alleles for a characteristic
Dominant
The gene that is expressed in the phenotype of a heterozygous individual
Recessive
The gene that is masked (not expressed) in the phenotype of a heterozygous individual
True breeding
A true breeding individual is homozygous for the characteristic
Most features of an individual phenotype are polygenic and show continuous variation.
Polygenic
A characteristic that is controlled by many genes is described as polygenic.
Characteristics showing continuous variation are polygenic.
Most of an organism’s characteristics are polygenic
Two parents with the characteristic resulting from the dominant gene can produce offspring (children) with the
recessive characteristic
But
Two parents with the recessive characteristic cannot produce offspring with the dominant characteristic
Male with attached ear lobes
Male with free ear lobes
Female with attached ear lobes
Which characteristic is controlled by the dominant gene?
An individual with the recessive characteristic must have two recessive genes
What is the genotype of the son who has free ear lobes?
An individual receives one gene for a characteristic from each parent and passes one gene for each
characteristic on to each offspring
What is the genotype of the two parents?
Transport in plants – what the syllabus says you should know
Plant transport systems
i.
Water is required for transporting materials and for photosynthesis.
ii.
Structures and processes involved in water movement to include root hairs, guard cells, stomata,
epidermis, mesophyll cells and transpiration
•
•
•
•
Transpiration is the loss of water through leaves.
Water is lost by evaporation through stomata.
Opening and closing is controlled by guard cells, which are found in the leaf epidermis.
Mesophyll cells of the leaf require water for photosynthesis.
Water and minerals are transported up through the stem in xylem.
Xylem cells are lignified.
• Xylem cells are lignified to withstand the pressure changes as water moves through the plant.
iii Sugar is transported up and down the plant in living phloem cells.
Water is required for transporting materials and for photosynthesis.
Plants need water
1. To transport dissolved substances such as minerals
2. As a raw material for photosynthesis
Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis,
mesophyll cells and transpiration
Root hairs
Root hairs are extensions of cells on the outer layer of the root (called the epidermis)
Root hairs
1. Anchor the root in the soil
2. Increase it’s surface area for absorbing water
Root hairs
Guard
cells
Guard cells
A leaf has pores called stomata mainly on it’s
lower surface.
Each pore (stoma) is surrounded by 2 guard
cells.
Guard cells control the opening and closing
of the stomata.
The guard cells are part of the epidermis
tissue of the leaf.
stoma
Epidermis
cells
Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis,
mesophyll cells and transpiration
Diagram showing guard cells surrounding the stoma
Stoma
Guard cell
Epidermis
cell
Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis,
mesophyll cells and transpiration
Leaf cells
The photo shows the layers of cells in a plant leaf
This part contains palisade
mesophyll cells where most
photosynthesis in the leaf takes
place
This part contains spongy
mesophyll cells where some
photosynthesis takes place
Water and minerals are transported up through the stem in xylem.
Xylem cells are lignified to withstand pressure changes as water
moves through the plant
Xylem
Water is transported from the roots up through the plant
to the leaves in tubes called xylem vessels
Xylem vessels are lignified – this means they have a substance called lignin
in their walls, usually in the form of lignin rings
Lignin allows the vessels to cope with pressure changes as water moves
through the plant.
Xylem also transports minerals dissolved in the water and in addition helps
to support the plant.
Xylem vessels are made from dead cells
Xylem vessels showing
lignin rings
Transpiration is the loss of water through leaves.
Water is lost by evaporation through stomata.
Opening and closing is controlled by guard cells, which are found in the leaf epidermis.
Mesophyll cells of the leaf require water for photosynthesis.
Transpiration
Diagram of leaf cells
Transpiration is loss of water through the stomata of the leaves
Palisade and
spongy
mesophyll
cells
1. Water evaporates into air spaces in the leaf
2. Water diffuses out of the leaf through the stomata
Opening and closing of the stomata is controlled by the guard cells
The stomata are open in light and closed in darkness
Transpiration helps to pull water up from the roots to the leaves
The leaf mesophyll cells need the water to carry out photosynthesis
1
Guard cell
2
Movement of water through the plant
Water enters leaf cells
Water evaporates from leaf
cell surface into air spaces in
the leaf
Water vapour diffuses out of the leaf
Water enters root
hair cell from soil by
osmosis
Water is drawn up through the
xylem vessel by transpiration in
the leaf
Water passes across the root from cell to
cell and into a xylem vessel by osmosis
Loss of water through the stomata is called
transpiration
Sugar is transported up and down the plant in living phloem cells.
Phloem
Phloem is a plant tissue composed of living cells in which sugar is transported
Phloem has two types of cells
• Sieve tubes
• Companion cells
Perforated
sieve plate
Sieve tubes have no nucleus and their separating walls (called sieve plates)
have holes that allow strands of cytoplasm to run from one cell to the
next.
Companion cells have a nucleus and they control the sieve tubes.
Sugar moves through the sieve tubes from the leaves where it is made by
photosynthesis to other parts of the plant where it is used for respiration or to
parts where it is stored, e.g. fruits.
Sieve tube
Companion cell
Heart – syllabus content
Multicellular organisms need transport systems to deal with surface area to volume
ratio issue.
Animal transport and exchange systems
In mammals, nutrients, oxygen and carbon dioxide are transported in the blood.
Pathway of blood through heart, lungs and body.
Heart structure to include right and left atria and ventricles.
Blood vessels to include: aorta, vena cava, pulmonary arteries and veins, and coronary arteries.
Arteries have thick, muscular walls, a narrow central channel and carry blood under high pressure.
Veins carry blood under low pressure; have thinner walls and a wide channel.
Veins contain valves to prevent backflow of blood.
Capillaries form networks at organs and tissues, and are thin walled and have a
large surface area, allowing exchange of materials.
Red blood cells contain haemoglobin and are specialised to carry oxygen
Heart structure to include right and left atria and ventricles.
Structure of the heart
Chambers of the heart
Left atrium
Right atrium
Right ventricle
Left ventricle
Note: The left ventricle has a thicker wall (more muscle in its wall) than the right
ventricle because it pumps blood further
Blood vessels to include: aorta, vena cava, pulmonary arteries and veins, and
coronary arteries.
Blood vessels entering and leaving the heart
Blood to the body
Pulmonary artery
Blood to the lungs
Aorta
Vena
cava
Blood from
the lungs
X x
Position of
heart valves
Blood coming from the body
X
X
Pulmonary vein
Blood supply to the heart itself
The heart tissue receives blood from the coronary arteries
Right
coronary
artery
Left
coronary
artery
Arteries have thick, muscular walls, a narrow central channel and carry blood under high
pressure.
Veins carry blood under low pressure; have thinner walls and a wide channel.
Veins contain valves to prevent backflow of blood.
Vein structure
Artery structure
Thick layer
containing smooth
muscle
Thin layer
containing
smooth muscle
Narrow
channel
Wide channel
Arteries
Veins
Take blood away from the heart
Take blood back to the heart
Have thick muscular walls and a
narrow lumen - blood is under high
pressure
Have thin walls and a wide
lumen - blood is at low pressure
No valves
Have valves to prevent backflow
of blood
Capillaries form networks at organs and tissues, and are
thin walled and have a large surface area, allowing
exchange of materials.
Capillaries
Capillaries are very small, thin walled vessels that are found close to all body cells
Substances are exchanged between the blood and cells through the capillary walls
Capillary beds
Body cells are found close to capillaries
in capillary beds
Substances like glucose and oxygen pass by
diffusion from the blood in the capillaries to the
liquid around the cells then into the cells.
Carbon dioxide diffuses in the other direction
Glucose and oxygen
Carbon dioxide
capillary
Tissue fluid
Body cells
Capillaries have a large surface area and thin walls to allow efficient exchange of
substances
Red blood cells contain haemoglobin and are specialised
to carry oxygen
Oxygen is transported in red blood cells
Red blood cells contain a substance called haemoglobin.
When the oxygen concentration is high (in the lung capillaries), haemoglobin
joins with oxygen to make oxyhaemoglobin
Oxygen is carried in the blood joined to haemoglobin
When the oxygen concentration is low (in the body capillaries) oxyhaemoglobin
breaks down again to release the oxygen for the body cells.
in lung capillaries
Haemoglobin + oxygen
in body capillaries
oxyhaemoglobin
National 5 Biology Course Notes
Unit 2 : Multicellular Organisms
Part 8 : Effect of lifestyle choices on
animal transport systems
These lifestyle choices can have a harmful effect on the heart and blood vessels
1.
2.
3.
4.
5.
6.
A high fat diet
A high salt content in the diet
Lack of exercise
Smoking tobacco
Excessive alcohol drinking
Stress
These directly and indirectly increase the chance of fat deposits forming in blood vessels, blood clots, heart
attacks, strokes and type II diabetes.
Fat deposits in artery walls narrow the vessels and restrict blood flow.
This and blood clots block arteries stopping blood flow and causing
heart attacks and strokes
Anaemia
The mineral iron is needed to make haemoglobin.
Deficiency of iron in the diet leads to anaemia.
Environmental factors
Environmental factors which pose hazards to our health include;
1. Toxic heavy metals which are found in paint, fuel and old pipes.
2. Carbon Monoxide pollution via vehicle exhausts, faulty gas mains or fires in homes.
3. Radiation from unprotected exposure to the sun including the use of sunbeds.