Biology – Module 2 – Patterns in Nature

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 multi-cellular 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 absorb water and mineral salts in plants.

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 C6H12O6 + 6O2

Chlorophyll

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 root tip has a root cap which protects the end of the root as it pushes through the soil. The root cap is being constantly worn away and 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 and are important in mechanical digestion as they break food up into small pieces by biting and chewing. The smaller pieces of food have a greater surface area to volume ratio and this means that digestive enzymes have a greater ability to work effectively. The teeth differ in size, function, arrangement and structure.

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:

· the chemical composition of their diet

· 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:

· root hair cells

· xylem

· phloem

· 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.