Biology – Module 2 – Patterns in Nature
3. Plants and animals have specialised structures to obtain nutrients
from their environment.

identify some examples that demonstrate the structural and functional
relationships between cells, tissues, organs and organ systems in multicellular organisms
There are a vast array of cells in our bodies, and each type has its own specific
function. A group of cells that perform the same function is known as a tissue, a group
of tissues that perform the same function is known as an organ, and a group of organs
that interact in order to carry out a function is known as a system.
Different cells have different purposes, such as cells involved in the exchange of
substances have special features in order to increase their surface area to volume
ratio, allowing them to function more efficiently. For example:
- cells may be flattened (eg. In tissue lining of the airs sacs in the lungs)
- the exposed edges of the cell may be folded, eg. Root hair cells that
water and mineral salts in plants.
absorb
Cell differentiation and specialization – In multicellular organisms, different types of
cells (tissues) are created specifically so that they carry out different functions.
Young cells (called embryonic cells) divide and five rise to new cells. When these cells
become specialised to perform a particular function, they are said to differentiate.
Once they have specialised to form a particular type of tissue, differentiated cells will
lose
their
capacity
to
develop
into
other
types
of
cells.
Undifferentiated cells that are able to divide into other types of cells are informally
known as stem cells.
A group of cells that is similar in structure and works together to carry out a common
function is called a tissue. Just as similar specialised cells that perform a common
function are arranged together to form tissues, so groups of tissues collectively form
organs.
An organ is an arrangement of different types of tissues, grouped together for some
special purpose; for example, the leaf is an organ for making food in a plant and the
heart is an organ for pumping blood in animals.
A system is a collection of organs that all work together to achieve an overall body
function, for example the digestive system or nervous system in animals and the
transport system in plants or animals.
A multicellular organism is a living plant or animal composed of many systems which
function together co-operatively to ensure its survival. When one or more of these
systems malfunctions, the organism is no longer healthy and disease or even death
may result.

distinguish between autotrophs and heterotrophs in terms of nutrient
requirements
Living organisms need to obtain nutrients in the from of organic nutrients such as
glucose, amino acids, fats, glycerol, vitamins, nucleotides as well as inorganic
nutrients such as minerals and water.
Organic nutrients are the main supply of stored energy in living things but are also
used in the structures of cells. Inorganic nutrients are essential as structural parts of
cells and tissues and they play an essential part in assisting enzymes in reactions but
they are not an energy source.
Organisms that can make their own food are called autotrophs. They are able to make
their own food by trapping energy from some other system and putting it into simple
molecules, which are then made into the sugar glucose. Organisms that trap energy
from the sun are said to carry out photosynthesis and those that trap energy from a
chemical reaction carry out chemosynthesis. This relies on using energy from
breaking chemical bonds to power their food-making, rather than using light energy as
do photosynthetic organisms.
Green Plants, cyanobacteria and a small number of other bacteria are photosynthetic
autotrophs. Bacteria that make their own food without light are called chemosynthetic
autotrophs and they are found on ocean floors where they trap energy from the
reactions of the compounds that are released from the cracks in the floor.
All other organisms are heterotrophs. They cannot make their own food and rely on
plants or other heterotrophs (that have eaten autotrophs) for their own food. Animals,
fungi and most bacteria are heterotrophs.
All living things require energy in order to survive. The energy that is required by all
living cells is a type of energy known as ATP (Adenosine Tri-phosphate). The energy of
ATP powers all cellular activities. The energy is released when glucose is broken down.
This process is known as cellular respiration.

identify the materials required for photosynthesis +its role in ecosystems
Requirements for photosynthesis:
Carbon dioxide, water, chlorophyll and light are all essential for the chemical process
of photosynthesis.
The water and carbon
dioxide which are used by
the plant during
photosynthesis provide
the basic chemical
“building blocks” of which
the resulting sugar is
made. Oxygen is given
out as a product as well.
The energy conversion
involves a change from
radiant energy (sunlight
or artificial light) to
chemical energy (stored in
glucose).
The role of photosynthesis in ecosystems:
Photosynthesis is the initial pathway by which energy enters all ecosystems.
Organisms that photosynthesis are producers. These organisms form the basis of all
food webs, without them there would be no life as no organism would be able to
harness the sun’s energy thus they would all perish. Glucose can be converted by
plants
into
other
organic
compounds
for
storage.
Glucose may be converted into and stored as:
 Lipids ( Sunflowers and Avocados store their food as oils)
 Proteins (legumes such as beans and peas)
 Carbohydrates (Potatoes)
These organic compounds, which rely on photosynthesis for their production, provide
the structural basis of living cells and also provide a source of energy for all cellular
purposes.
Atmospheric gases that are essential to living organisms are recycled during
photosynthesis. Eg. The process provides oxygen for the respiration all living things
and also removes Carbon dioxide from the atmosphere, thus reducing the effect of the
global warming situation.
Furthermore, fossil fuels were formed from photosynthetic organisms approximately
300 million years ago. Large plants were buried and over the thousands of years, as a
result of pressure, they turned into coal /oil /natural gas which all serve as sources of
fuel for us today.

identify the general word equation for photosynthesis and outline this as a
summary of a chain of biochemical reactions
The general word equation of photosynthesis:
Light
Carbon Dioxide + Water
Glucose + Oxygen
Chlorophyll
Light
6H2O + 6CO2
Chlorophyll
C6H12O6 + 6O2
Photosynthesis can be summarized as a chain of biochemical reactions that take place
in the chloroplasts of green plant cells +the cells of some photosynthesising bacteria.
Photosynthesis takes place in two main stages (where each stage is not a singular
reaction but rather, it consists of a series or chain of reactions):
-
The Light Phase (photolysis) involves the splitting of water using the
energy of light
The Light-Independent phase (Carbon fixation stage) involves using
carbon dioxide to make sugar, in the absence of light.
The Light Phase: Light energy from the sun is captured by chlorophyll in the
thylakoids in the grana of chloroplasts. The energy is used to remove an electron from
a chlorophyll molecule. Once these thousands of electrons have been removed, they
can be used for one of two purposes. Firstly, they can be used to decompose water or
secondly, they can be used to from ATP.
The Light-Independent Phase: This phase involves the use of Carbon Dioxide. In
this stage, the hydrogen atoms (produced during the decomposition of water) are
carried to the stroma.
-
Carbon dioxide is needed for this reaction and is absorbed by the plant via the
air. The hydrogen atoms along with carbon dioxide undergo a series of
enzyme controlled reactions to from sugar molecules
-
This cyclic cycle as shown in the diagram is known as the Calvin cycle.
-
The glucose is then converted into starch which is then stored in the plant.

explain the relationship between the organisation of the structures used to
obtain water and minerals in a range of plants and the need to increase the
surface area available for absorption.
Roots are the structures in plants that absorb water and other inorganic minerals from
the Earth. These structures have a significant surface area which allows water and
inorganic mineral salts to be absorbed efficiently. The epidermis is the outermost
layer of the plants organs and it is through this layer that the transfer of minerals and
water will occur.
Plants need to absorb a large amount of water at rapid rates in order to maintain a
balance within them. The uptake of water through the roots is through osmosis.
Osmosis is typically a slow process but it is speed up in this case due to the large
amount of surface area present in the plants root system.
The uptake of minerals through the roots is through diffusion. They are dissolve in
water (as they are ions) and they are absorbed by the plant when in this form.
Diffusion is too slow to meet the needs of the plant. A process known as facilitated
diffusion and active transport is involved, where the plant uses energy to draw in
water and mineral ions towards itself.
Increasing Surface Area: The surface area of any root system is multiplied by the
factor of twelve due to the presence of root hairs. These microscopic hairs vastly
increase the area by which water can diffuse into the plant. Another process can
increase the surface area of the root system and this is known as extensive
branching. In this case the roots may branch off in one of three ways, thus forming
either a tap root system (one main root and then subdivisions occurring from that) or
fibrous root system (many branches subdivide).
Root Structure:
The
end
The
and
root tip has a root cap which protects the
of the root as it pushes through the soil.
root cap is being constantly worn away
hence is constantly being replaced.
Just behind the root cap is meristematic
tissue where cell division constantly makes
new cells for growth. Behind this region is the
zone of elongation where the new cells get
longer causing the root to push out through
the soil. Root hairs are produced behind these
layers (through the epidermis). Once water is
absorbed through the root hair is passed into
the xylem in the vascular bundle inside in the center of the root. Inside the xylem, the
water travels up the leaves.

explain the relationship between the shape of leaves, the distribution of
tissues in them and their role
Leaves are the main organ for photosynthesis in flowering plants, although
photosynthesis is not restricted to the leaves. Photosynthesis can occur in any green
part of a plant. The shape of leaves and the tissues inside the leaf are related to this
role of photosynthesis.
A typical leaf has a petiole (leaf stalk) and a flattened blade which is usually thing
and broad with a system of veins providing transport for water and sugars. Leaf shape
and size for most plants can be related to the native environment of that species. For
example plants found in rainforests have large, broad, flat leaves to capture as
much sunlight as possible in the light restricted environment, which has plentiful water
supply. On the other hand desert plants receive high sunlight but many plants have
leaved that have reduced surface area or rolled into cylinders to reduce water loss
through transpiration.
Each species has an ordered way in which the leaves are arranged on the stem. This
pattern ensures that each leaf receives sunlight so it can photosynthesise. The leaves
can be arranged either alternately, opposite or in a whorl.
The upper and lower surface of a lead ha a layer called the epidermis. The epidermis
is a transparent layer that allows sunlight to pass through for photosynthesis.
Epidermal cells fit closely together to reduce evaporation from the leaf and stop
bacteria and fungi from entering. Occasionally, the epidermis is covered in a thin waxy
cuticle.
Stomates are found in the epidermis, with more stomata located on the lower
epidermis. Each stomate consists of two guard cells and a pore which opens
depending on sunlight/water availability.
Mesophyll tissue lies between the upper and lower epidermis. The top zone contains
the palisade mesophyll (which contains chloroplast, this is why they are stacked
tightly together – so that they can maximize the photosynthesis that occurs). The
lower zone contains spongy mesophyll, these are responsible for the gaseous
exchange that occurs within the leaf.
Vascular bundles (veins) are also found between the upper and lower epidermis.
Vascular bundles contain xylem tissue which delivers water and mineral ions up the
plant. Phloem tissue which removes sugars, and cambium tissue which is
meristematic tissue with cell division making new xylem/phloem.
The role of leaves:
-

to absorb sunlight and carbon dioxide during the day
to release oxygen
to provide chlorophyll for photosynthesis
to make glucose and transport it to other parts of the plant where it can be
stored as starch or other organic molecules
to transpire (release water) in order to cool down the plant and also to create
a suction pull to lift water from the roots to the top of the plant.
To provide a medium for which products / reactants of photosynthesis /
respiration can be obtained or released.
describe the role of teeth in increasing the surface area of complex foods for
exposure to digestive chemicals
Teeth are found in the mouth of vertebrates
digestion as they break food up into small pieces
pieces of food have a greater surface area to
digestive enzymes have a greater ability to work
function, arrangement and structure.
and are important in mechanical
by biting and chewing. The smaller
volume ratio and this means that
effectively. The teeth differ in size,
Each type of tooth has a specific function. Incisors are chisel-shaped teeth at the
front and are used for biting. Canines have a sharp point and are used for tearing
meat. Premolars have sharp cutting edges and are used for crushing food. Molars
have large flat surfaces with blunt ridges are used for grinding food.
When food enters the mouth, the salivary glands release saliva into the mount
chewing mixes the saliva with the food. Saliva has several functions. It dissolves some
of the food, helps to lubricate the food and makes some small pieces stick together.
Human saliva contains a digestive enzyme known as salivary amylase which splits
starch into units of disaccharide maltose. When food is swallowed the acid in the
stomach inactivates the salivary enzyme. When the teeth break down the food, they
increase the surface area to which the enzyme can get to.
The structure, locations and numbers of teeth can show the diet of a particular
organism. For example
Herbivores: have incisors that are used to bite off vegetation. They also have
specially adapted molars that are broad and crushing. They are specially equipped with
ridges to help break open the cellulose cell walls of plants. It is extremely difficult to
break down the cellulose physically or chemically. Furthermore, plants do not provide
large amounts of energy for the herbivore, so they must eat for long periods of time.
Their teeth are adapted to these situations. Many herbivores have microbes in their
gut which increases the rate at which the cellulose is broken. Canine teeth are absent
in the herbivore.
Carnivores: They have powerful jaws and well-developed canine teeth, conical in
shape and they are specialised for holding and killing prey and tearing meat from the
bones. The meat is torn off in chunks and they have molars with large cusps that
briefly chew the meat before digestion.
Smaller carnivores (that are adapted to feed on insects) have teeth adapted for
piercing and penetrating the tough cuticle of their prey. They have to puncture the
exoskeleton with their premolars and then use these teeth to shear the inner tissues.

explain the relationship between the length and overall complexity of
digestive systems of a vertebrate herbivore and a vertebrate carnivore with
respect to:
o the chemical composition of their diet
o the functions of the structures involved
The digestive system consists of the alimentary canal and its associated organs. The
alimentary canal is a long tube running from the mouth of to the anus where the
ingested food is broken down into smaller pieces so that nutrients can be absorbed.
Unneeded wastes are eliminated through the anus.
The digestive system produces enzymes to break down the ingested food. Digested
foods are absorbed through the walls of the alimentary canal. Amylase enzymes
break down carbohydrates to glucose. Protease enzymes break down proteins into
amino-acids. Lipase enzymes break down lipids into glycerol and fatty acids.
Most of the digestive food particles are absorbed through the villi of the small
intestine. The simple sugars, amino acids and mineral elements may diffuse across
the cell membranes, although most movement is by active transport. Amino acids,
carbohydrates and minerals are absorbed into the bloodstream, while fatty acids and
glycerol enter the lacteal which runs down the middle of each villi.
Absorption in the small intestine is efficient because it is a fairly long tube with
thousands of small projections called villi. These villi are covered with microvilli and
these structures increase the surface area for absorption. Other features which aid in
efficient absorption are the thinness of the epithelial lining and a rich blood supply in
each villus (singular for villi which is a plural).
In the bloodstream, the amino acids, sugars and minerals are carried to the liver by
the hepatic portal vein where the products of digestion may be stored or altered as
needed by the body.
Once in the lacteal, the fatty acids are recombined to form fats once again. The fats
are often coated with special proteins, becoming lipoproteins for transportation. The
lymphatic system transports the lipids from the digestive to the circulatory system.
Structure
Description + Function
Mouth
Teeth mechanically break food into small pieces. – increases surface
area
Saliva lubricates the food.
Amylase digests starch into smaller molecules of maltose.
Salivary Glands
Secrete saliva in order to moisten the food for easy swallowing and
begin the chemical digestion and break down of the food (starch).
Epiglottis
This closes off the windpipe so that food goes down the oesophagus
rather than the wind pipe – which prevents choking.
Pharynx
Muscular walls surrounding the opening of the oesophagus in order to
swallow food.
Oesophagus
Peristalsis (the contraction and expansion of muscles in the
throat) moves the food down the oesophagus and carries it to the
stomach
Liver
Produces bile that emulsifies fat - released into duodenum. Center of
metabolism – controls start / end products of digestion, makes urea
from amino acids.
Gall Bladder
Stores the bile
Stomach
Proteases begin the digestion of proteins. It has a thick strong
muscular wall with a mucus lining to protect it from the acid inside.
Churns the food by involuntary muscle contraction, mixing it with
digestive juices.
Pancreas
Produces enzymes which are released into the duodenum of the small
intestine, also produces insulin which controls the blood glucose level.
Small Intestine
Digestion is completed by enzymes from the pancreas and the small
intestine itself. This is also where the absorption of nutrients occurs
(through villi). Its inner walls are greatly folded to increase the
surface area for absorption. Long narrow tube, greatly coiled,
between the stomach to the large intestine. Increases the time that
the food remains there for absorption.
Appendix
Plays no role in the human digestive system
Large Intestine
Water is absorbed with soluble compounds, like vitamins and
minerals.
Undigested food leaves the body as faeces.
Rectum + Anus
Rectum (last part of the large intestine) stores the undigested
material, while the anus egests that material.
The diet of the animal determines several features of their digestive system.
Plant material has fewer concentrated nutrients than meat so herbivores need to each
much more food each day when compared to carnivores. Since plant cells has a
cellulose cell wall which is hard to digest, the plant material needs to stay longer in the
digestive tract in order for successful digestion.
An increase in the length of the digestive tract provides space to hold the large
quantity of food that must be eaten, gives the maximum opportunity for microbial
action to take place and allows time for the nutrients to be absorbed. The increased
complexity is evident by the presence of highly specialised digestive organs which are
necessary to break down the high-fibre diet.
Thus, it follows, that generally herbivores has a longer alimentary canal relative to
their body size than carnivores.
Many herbivores have special chambers where the bacteria and protests live and make
enzymes that can break down cellulose into usable sugars. These fermentation
chambers can be before the stomach, and these animals are known as foregut
fermenters, or the chamber can be after the small intestine and these animals are
known as hindgut fermenters.
Ruminant Herbivores such as cows are foregut fermenters. They have stomachs
with four chambers. The food will pass into the first chamber called the rumen, where
it is broken into smaller pieces. Usually it cannot leave the rumen until it is about 1mm
long. The contents of the rumen can be regurgitated into the mouth as ‘cud’ which are
then re-chewed, mixed with more saliva and passed back into the rumen.
The micro-organisms ferment the food, which turns the plant material into a useful
form that can be used by the host. They also produce amino acids. These are not
part of the diet, but it forms a symbiosis as both organisms benefit from the
association.
Hindgut Fermenters have an enlarged caecum. This usually forms a blind ended sac
between the intestines. The caecum contains microorganisms with ferment the
cellulose in the plants. Some of the products of digestion can pass directly through the
wall of the caecum to the bloodstream, but many hindgut fermenters eat their faeces
so that the food passes twice through their body and so they can obtain vitamin B-12.
Carnivores eat meat, which is predominantly protein which requires less digestion.
The acid in the stomach breaks down some muscle and tissue and the protease
digestive enzyme, eg. Pepsin breaks down the peptide bonds in protein. The fats in the
meat are not broken down until the food reaches the small intestine, where bile from
the liver and lipase enzymes from the pancreas + walls of the small intestine break
down the lipids. Protein and fat contain more energy than plant material (per gram),
thus carnivores eat less to gain same amount of energy.
Carnivores have a simple stomach (which may be enlarged to store food), a short
intestine relative to their body size and the caecum may be absent or, if present,
greatly reduced in size.
Adaptations for feeding are thought to be one of the main forces behind the
evolutionary process. If an adaptation in an organism makes it easier for them to
obtain food or allows them to obtain nutrients from a type of food not sought by
others, it is to their advantage because competition is reduced.
4) Gaseous exchange and transport systems transfer chemicals through the
internal and between the external environments of plants and animals.

Compare the roles of respiratory, circulatory and excretory systems
Respiratory System
Individual cells obtain energy by the process of respiration. During aerobic respiration
organic molecules such as glucose are combined with oxygen to release energy, and
carbon dioxide and water are formed as the waste products.
However, for respiration to occur, organism need to be able to supply oxygen to the
cells and remove carbon dioxide. Gas exchange is the movement of oxygen and
carbon dioxide in different directions across the membrane.
Respiratory surfaces where gas exchange occurs requires several features:
Respiratory surfaces must be moist so oxygen and carbon dioxide can
dissolve so oxygen and carbon dioxide can dissolve, in order to diffuse
across the membrane.
They need a large surface area for maximum diffusion.
They need a rich blood supply to remove the oxygen once it has been
absorbed so more oxygen can be absorbed.
They need to be thin to reduce the amount of diffusion needed.
The respiratory system enables organisms to take in oxygen and remove carbon
dioxide from their bodies – it allows for gaseous exchange between the organism and
its external environment. Oxygen is essential for almost all living organisms as it is
needed for the release of energy from food during cellular respiration. Carbon dioxide
is a waste that must be removed as it is toxic in large quantities.
The respiratory system is made up of tissues and organs that are specialised for
gaseous exchange. In animals the respiratory organs are varied, such as lungs in
mammals, gills in fish, tracheal systems in insects. In plants however, the respiratory
tissues include stomates and lenticels.
Circulatory System
The circulatory system is another name for the transport system in animals. It carries
substances needed by the body from their point of entry into the body to the parts of
the body where they will be stored or used. In animals, nutrients are carried in a fluid
medium (most often blood) that circulates around the body, picking up and dropping
off chemicals. This type of transport system is therefore termed a circulatory system.
Effective circulatory systems have the following properties:
a system of vessels in which substances are transported
some way of ensuring the materials flow in the correct direction
a medium in which the chemicals are carried
a mechanism to ensure substances are released where they are needed.
The role of the circulatory system:
Transport of gases (oxygen and carbon dioxide), nutrients, waste products,
hormones and antibodies
Maintenance of a constant internal environment
Removal of toxins and pathogens
Distribution of heat
Excretory system
Excretion involves expelling metabolic wastes from the body—wastes that have been
made by cells as a by-product of metabolism.
The role of the excretory system:
To remove metabolic wastes from the transport medium (eg blood) and to
expel them outside the body. This includes nitrogenous wastes and carbon
dioxide.
Help maintain water balance. For example the more toxic the waste, the more
amount of water is required for dilution before excretion.
In some organisms it can also be used in the elimination of excess salt, and
also regulation of pH
Note: There is no official recognized excretory systems in plants.

identify and compare the gaseous exchange surfaces in an insect, a fish, a frog
and a mammal
Human Respiratory System
In humans, air enters the nostrils, travels to the pharynx and then to the trachea
(windpipe). The epiglottis is a small flap of tissue that prevents food from entering the
trachea. The trachea then splits into two bronchi which enter each lung and branch
into smaller tubes called Bronchioles. Bronchioles end in air sacs called alveoli which
have thin epithelium surrounded by a network of capillaries for gas exchange.
Fish Respiratory System:
The respiratory system of a fish need to be more efficient than that of humans as
there is less oxygen in water than in air, and diffusion is slower in liquids than in air.
Furthermore, warm water holds less oxygen than cold water.
In fish, the respiratory organs is the gills. The gills are usually protected by an
operculum (or gill cover). Most fish have four gill arches on either side of the head and
each arch has two rows of gill filaments which are covered with gill lamellae. To
increase the efficiency of gas exchange the fish keeps a constant flow of water moving
across the gill filaments. The water is gulped in through the mouth and then the
movement of the operculum causes the water to be pushed through the buccal cavity,
across the gills and out the other side past the operculum.
The flow of blood in the capillaries is in the opposite direction to the flow of water. This
creates a diffusion gradient and is called a countercurrent arrangement. This
increases efficiency so that up to 95% of oxygen can be obtained from the water.
Frog Respiratory System
The skin of many amphibians is used as a respiratory surface. This is why they need to
be in moist environments so that their skin remains moist. Frogs have very simple
sack like lungs which are connected to the buccal cavity. Different frogs have different
ways of getting air into their lungs. Frequently the skin is the site of carbon dioxide
loss and the lungs are involved in oxygen absorption.
Insect Respiratory System
Insects have an exoskeleton made of chitin that is often coated in a thin layer of wax.
This is impermeable and does not allow gas exchange, and thus insects need a system
to allow gases in and out of their body.
Their respiratory system is known as a tracheal system and consists of holes called
spiracles that form a row along both sides of their body. The spiracles connect to a
series of tubes called tracheae, which can be strengthened with chitin. The tracheae
lead into smaller tubes called tracheoles which reach to the surface of most cells of the
body where gas is exchanged.

explain the relationship between the requirements of cells and the need for
transport systems in multicellular organisms
As we already know, unicellular organisms are so small that their surface area to
volume ratio is adequate to allow them to rely on simple diffusion to supply
requirements such as oxygen for cellular respiration and to remove waste products
such as carbon dioxide, urea and other metabolic wastes. Water levels can also be
maintained simply, through the passive process of osmosis across the body surface,
because the surface area to volume ratio of these organisms is large enough.
Multicellular organisms are bigger in size and so their total surface area to volume
ratio is smaller. Cells near the center of these organisms would be too far away from
the surface for substances from the outside environment to reach them efficiently
(remember, diffusion and osmosis are slow, passive processes). Large organisms that
are active, such as complex animals, need more nutrients and oxygen to provide them
with energy and they produce more wastes, so they have a greater need for transport.
This problem is solved by the presence of a transport system within the bodies of large
multicellular organisms.

outline the transport system in plants, including:
o root hair cells
o xylem
o phloem
o stomates and lenticels
Root Hair Cells:
Each root hair is an extension of an epidermal cell in the root. The structure of the root
hair greatly increases the surface area available for the absorption of water and
mineral ions. The root epidermis is not covered in a waxy cuticle like the leaf
epidermis, as the roots needs to be able to allow water to be easily absorbed across its
surface. The inside of a root hair is mainly vacuole with a thin layer of cytoplasm lining
the sides.
Water usually enters the root hair by osmosis which is passive transport, however
under certain conditions the plant may use energy actively secrete water inwards
causing water to be absorbed faster than by simple osmosis.
Once the water has entered the root hair, it can either move through the cells or
between the cell walls and through the intercellular spaces. In the root the Casparian
strip is a layer of wax around the endothermic which blocks movement through cell
walls, allowing to control the movement of materials into the center of the root where
the xylem is situated. Thus the endodermis, with the Casparian strip prevents
the backflow of water and maintains root pressure.
Gaseous exchange between roots and soil also takes place, relying on diffusion of
gases. Cells of the root cannot photosynthesise (they are not exposed to sunlight and
have no chlorophyll) but they do respire like all living cells.
Xylem
Xylem transports water and inorganic ions up the plant from the roots to the leaves.
Xylem tissue consists of several types of cells, eg. Tracheids, which are long thin cells
with tapered, interconnected walls, and xylem vessel cells, which do not have end
walls and form longer tubes.
The walls of the Tracheids and xylem vessel cells have pits to allow the sideways
movement of water in or out of the xylem.
Lignin thickening on the walls of the xylem vessels provides structural support.
Movement of water in the xylem is due to a number of factors. Fore example, root
pressure from the inward movement of water into the xylem forces water up the stem.
However the main force is C.A.T
1) C – Cohesion – This refers to the water molecules natural ability to resist
separation from one another. The water molecules when pulled upwards,
drag the others below them as well.
2) A – Adhesion – This refers to the ability of water molecules to stick to
surfaces. The water molecules stick to the walls of the xylem.
3) T – Transpiration Pull – This refers to the force caused by the evaporation
of water out of a stomate so water is pulled up as a result in order to
maintain the continual stream of water in the plant.
Note: Water not only moves up the plant but moves laterally across it as well.
Phloem
Phloem consists of sieve tubes with sieve plants at either end companion cells. The
sieve tubes are arranged into a tube shape, one on top of the other and have no
organelles.
Companion cells are located along each sieve tube and it is believed the organelles in
the companion cells also service the sieve tube.
Phloem carries organic material, such as sugars, up and down the plant. The
movement of sugars around the plant is called translocation. The pressure flow of
phloem tap model is used to explain the movement of materials in the phloem.
Sucrose entering the sieve tube creates a high solute concentration, which causes
water from adjacent xylem vessels to enter the sieve tube so the pressure increases.
Removal of sucrose which create low pressure, the sap thus moves from a region of
high pressure to a region of low pressure.
Stomates and Lenticels
Stomates are numerous small openings in the surface (epidermis) of plant leaves and
stems through which gases enter and leave. In leaves, stomates open into the spongy
mesophyll where the air spaces allow gases to quickly reach of leave cells. During the
day, while the plant is photosynthesising, carbon dioxide will diffuse into the mesophyll
cells and oxygen will diffuse out. However opening a stomate will result in water loss
and this can lead to the dehydration of the plant. Stomates will thus close to reduce
water loss despite ideal photosynthesising conditions.
Stomates consist of two guard cells and a pore. Guard cells control the opening
and closing of the stomate. The movement of water into the guard cell makes the cell
turgid and it will expand causing to pore to open, while the movement of water out of
the guard cell makes it flaccid which results in the pore closing.
Lenticels small opening found in the roots or bark of stem of woody plants that allows
gases to be exchanged with the atmosphere.
Lenticels provide a place of gas exchange through the bark. On woody stems, the
lenticels appear as raised dots. They consist of loosely arranged cells with lots of air
spaces around them. They are essential for gas exchange.

compare open and closed circulatory systems using one vertebrate and one
invertebrate as examples.
A closed circulatory system is where the circulating fluid is always contained in a
set of blood vessels
An open circulatory system is where the circulating fluid oases through blood
vessels that open into interstitial spaces.
Closed Circulatory Systems
Closed circulatory systems are found in vertebrates and a few invertebrates such as
squids and worms. A heart, or a series of hearts, pump blood through blood vessels
and most diffusion of materials in and out of the blood vessels occurs in the thin walled
capillaries. Any fluid that seeps from the blood vessels into the extra-cellular fluid,
called the interstitial fluid, is collected by the lymphatic system and then returned to
the bloodstream.
In humans the circulatory system is called double circulation as the blood goes through
the heart twice in each circuit. Blood from the body enters the right side of the heart
and is pumped to the lungs where it is oxygenated. The blood is then returned to the
left side of the heart which pumps the blood out the aorta. The blood then travels
through the arteries which connect to the capillaries and then the veins which return
the blood to the heart.
Open Circulatory systems
These are found in many invertebrates eg. molluscs. The heart pumps the blood
through blood vessels which open into the interstitial places. Here the cells are bathed
in the fluid which gradually makes its way back to the heart where it is re-oxygenated.
The circulated fluid is not distinguishable from the interstitial fluid and is called
Haemolymph.
In the Grasshoppers circulatory system, the Haemolymph enters a dorsal tubular heart
from openings called ostia and is pumped through side vessels and forward through an
anterior vessel. It then moves into spaces in the body where materials are exchanged
with the cells. The Haemolymph is drawn back into collecting vessels which lead to the
heart.
Open System
Closed System
Haemolymph completes the circuit slowly
Haemolymph completes the circuit rapidly
Cannot meet the high needs of active
animals that have high metabolic rates
Can meet the high needs of active
animals that have high metabolic rates
Inefficient
Efficient
Exchange of materials is direct in an open
system between Haemolymph and body
cells
Exchange occurs across walls of capillary.
Heart does not have to be as powerful as
the fluid enters the interstitial space and
does not need powerful pumping through
small vessels.
Requires a stronger heart which has to
pump blood through thin tubes, requiring
higher pressure to overcome the
resistance to flow.
Exchange of materials is direct between
the Haemolymph and the body cell
Exchange of materials will occur through
the wall of a capillary.
Circulatory system in the grasshopper is
used to transport both nutrients and
wastes whereas the gas exchange occurs
in the trachea
Circulatory system transports gases as
well as nutrients and wastes. So the
added function of gas transport is present
This does not occur. Since they are not
differentiable.
Separation of interstitial fluid and
circulating fluid allows the blood to
develop properties.
In humans, the main difference between lymph (interstitial fluid) and blood contains
red blood cells which combines with oxygen to form oxyhaemoglobin. Haemoglobin
greatly increases the ability of blood to carry oxygen. Thus a unity volume of blood can
carry more oxygen for respiration that a unit volume of Haemolymph and more easily
meet the energy needs of the animal.
5. Maintenance of organisms requires growth and repair.

Identify mitosis as a process of nuclear division and explain its role
Mitosis is a process during cell division in which the cell nucleus divides in two. Mitosis
is needed to create new cells for growth, repair and reproduction. Since all organisms
begin life as one cell, a fertilised egg, mitosis is essential to become a multi-cellular
organism. Genetic information is transferred to new cells as DNA, which is present in
nuclei, mitochondria and chloroplasts. Mitosis increases the number the number of
cells. Even when the organism has ceased ‘growing’, mitosis is still needed. Older cells
need replacement as they are damaged or worn and some parts are continually
growing – like hair.

identify the sites of mitosis in plants, insects and mammals
In plants, meristematic tissues are the site of mitosis. Cells in the meristem
keep diving and producing new cells, some of which differentiate to become specialised
cells, while others stay in the meristem.
There are two types of meristems in plants – apical meristems are near the tips of
shoots and roots and increase the length of these regions, while lateral meristems
increase the width of the plant and make up the cambium, which provides new xylem
and phloem.
Many insects have a complex life cycle where the egg hatches and an immature form
called larva emerges. Often larva growth in size is due to cell enlargement rather than
division. The larva forms a pupa where the cells are called imaginal discs, which were
previously inactive. These now divide and larval cells break down. They increase in
number and size resulting in the adult form of the insect. The process is called
indirect development.
In mammals, cells are replaced over a period of time but some areas have mitosis
occurring most of the time. Eg. Skin is constantly replacing cells that are rubbed off,
the cell lining of the digestive systems is being replaced and bone marrow is constantly
making new blood cells. The growth pattern is direct development from juvenile to
adult with a change in body proportions and an increase in size.

Explain the need for cytokinesis in cell division
Cytokinesis is the division of the cell’s cytoplasm following the division of the nucleus.
Cytokinesis is important because it stabilizes the internal concentration of materials in
the two new cells. Each new cell needs sufficient organelles so that it can grow and
carry out the process of living.
In plant and animal cells: Cleavage occurs in animals cells as the cells are pinched into
two segments by a ring of contracting filaments which appear near the cell surface and
contract. Plants cannot do this as they have a rigid cell wall. In plants, a cell plate
forms during telophase across the mid-line of the parent cell. The plate grows
outwards, forming two membranes that become the two new cell membranes. The
new cell walls form between the membranes.
Cytokinesis is important to separate the newly formed daughter nuclei, to ensure that
each cell has only one nucleus. The outcome at the end of mitosis and cytokinesis is
two daughter cells that have the identical chromosomes to each other and to the
original parent cell.

identify that nuclei, mitochondria and chloroplasts contain DNA
When the cytoplasm divides, the organelles such as mitochondria and chloroplasts are
distributed to the daughter cells in approximately equal numbers. It is then necessary
for the organelles in the cytoplasm to replicate so that they are not reduced in
quantity. Assimilation is important in the growth of many organelles, but mitochondria
and chloroplasts contain their own small amounts of DNA and so they are able to
replicate themselves. By the time the daughter cells have grown to the size of the
original cell, they have a similar number of organelles as the original cell had.