Module 2: Organisation of Living Things

Organisation Of Cells

Inquiry Question- How are cells arranged in a multicellular organism?

  • Unicellular Organisms (Bacteria)

    1. Contain one cell, either prokaryotic or eukaryotic
  • First forms of life

  • A single cell carries out all life processes → obtaining nutrients, exchanging gas, removing waste and reproduction

  • High SA:V ratio which allows for more efficient movement of substances - Requires a moist environments for diffusion and osmosis to occur

  • Colonial Organisms (Volvox)

    1. A group of cells working or organism working collectively is called a colony
  • May be unicellular or multicellular

  • Can exist independently, however in a multicellular organism colonial organisms cannot exist alone.
  • Multicellular Organisms

    1. A community of cells working together to enable the organism to carry out life processes, including reproduction.
  • Composed of many different specialised cells, Similar cells are grouped together and perform specific functions that combine for the efficient functioning for the organism - Consists of eukaryotic cells.
  • Large organisms made up of smaller cells increases SA:V ratio.

  • Each specialised cell type is structurally suited to a particular function.

  • Embryonic cells develop suitable structural changes to best suit their function → Red blood cell

    1. When cells become specialised they differentiate – they develop structures enabling them to carry out their function, making them different to other cells.
  • Specialised cells originate from stem cells, which are undifferentiated cells with the ability to divide repeatedly.

  • [Cell specialisation refers to the function of the cell, while differentiation is the] [process of a stem cell goes through to become specialised.]

  • Enables organisms to grow larger while still efficiently carrying out processes.
  • Specialised cells cannot survive independently – they rely on other cells in the organisms to carry out functions they cannot.
  • Communication between cells is vital.
  • In animals this is via the bloodstream and nervous system whereas in the plants it is brought about by chemical and physical contact between cells.

  • Cell Hierarchy

    1. Organelle Cell Tissue Organ Organ System Organism
  • Mitochondria Cardiac Muscle Cell Cardiac Muscle Tissue Heart Cardiovascular System Human
  • Animal Tissues

    1. Epithelial Tissue
  • Covers body surfaces, protects organs and forms glands.

  • Densely packed cells in single sheets or layers.

  • Doesn’t contain blood vessels.

2 distinct surfaces – exposed to the exterior body cavity or exposed to adjacent tissue.

  • Some are specialised for absorption or secretion.

  • Connective Tissue

  • Provides support, ensures that all body parts are bound together and protects against damage

  • Fibrous connective tissue, loose connective tissue, adipose tissue, cartilage and bone → Differences are from the arrangement of cells and specialised structure.

  • Collagen (strength) + Elastin (Flexibility)

  • Nervous Tissue

  • Comprises brain, spinal cord and peripheral nerves.

  • Highly specialised for communication between all parts of the body

  • Highly specialised of passing messages between themselves and other cells
  • Muscle Tissue

  • Muscle cells are highly specialized for contraction

  • Skeletal, Smooth, Cardiac

  • Responsible for the movement of the body and particular contractions in various processes (oesophagus peristalsis)
  • Plant Tissues

    1. Meristematic Tissue
  • Tips of roots and shoots

  • Cells divide to produce new growth

  • Site of cell differentiation

  • Dermal Tissue

  • Protects plant tissue and is found in outer layers of stems, roots and leaves.

  • Epidermal layer is the outmost, secreting a waxy layer called cuticle, vital to reduce water loss

  • Lack Chloroplasts

  • Vascular Tissue

  • Responsible for the transport of substances around the plant

  • Xylem transports water and minerals from the roots to the leaves

  • Phloem transports products of photosynthesis around the plant

  • Ground Tissue

  • Internal cells of a plant other than the vascular

  • Specialised for storage, support and photosynthesis

Nutrient and Gas Requirements

Inquiry Question: What is the difference in nutrient and gas requirements between autotrophs and heterotrophs?

  • Autotrophs

    1. Produce their own organic compounds and energy from inorganic compounds from their environment, such as carbon dioxide and water.
  • Can be divided into two groups:

  • Photoautotrophs – use light energy (e.g. green plants).

  • Chemoautotrophs – use chemical energy (e.g. nitrifying bacteria in the soil)
  • Heterotrophs

    1. Obtain organic compounds from obtaining other organism
  • Include all animals and fungi

  • Vascular and Nonvascular Plants

    1. Majority of autotrophic organisms are plants.
  • Vascular plants possess a transport system to move substances from one part of the plant to another.
  • Plants have specialised cells grouped into tissues
  • These tissues work collaboratively to carry out life processes like photosynthesis and gas exchange.

  • A small number of plants are called non-vascular because they do not possess this transport system (e.g. mosses and liverworts). - Have a very simple structure.

  • All nutrients are absorbed, and wastes are removed by diffusion and osmosis through the surfaces of the plant.

  • Root System

    1. Usually underground.
  • The main function of anchoring the plant and absorbing water and inorganic nutrients from the soil.
  • Very large surface area.
  • Absorption occurs through specialised epidermal cells in the outermost layer of the root.
  • Increased surface area achieved in the following ways:

  • Extensive branching (also provides good anchorage)

  • Root hair zone located in the younger part of each root – epidermal cells protrude outwards into the surrounding soil, as microscopic extensions called root hairs.
  • Flattened epidermal cells increase the exposed surface.

  • Water moves via osmosis.

  • Mineral ions usually move via diffusion – if diffusion is too slow, facilitated diffusion and active transport may be involved.

  • Root cells have no chloroplasts and thus cannot photosynthesise, but they can carry out respiration

  • Shoot System (Stem)

    1. Provides structural support and a transport pathway
  • Located above ground

  • Consists of 3 main functions

  • Dermal→ Waterproofing, protection, gas exchange

  • Vascular → Composed of the xylem and the phloem within vascular bundles
  • Ground Tissue → Fills in around vascular tissue

  • Shoot System (Leaves)

    1. Located above ground
  • Main function is to absorb sunlight and carbon dioxide and produce glucose through the process of *photosynthesis.*​

  • Leaves are adapted to absorb the maximum amount of sunlight possible to provide the energy needed to break bonds in water during the first stage of photosynthesis.

  • Thin, flat structure of leaves is well suited to this function – no internal cell is too far from the light.

  • Large SA allows maximum absorption.
  • Transparent epidermis allows sunlight to penetrate the photosynthetic cells beneath.
  • Mesophyll​ is responsible for most of the plant's photosynthesis.

  • Palisade Cells: Dense with chloroplasts and are main

    photosynthetic cells, situated vertically, large numbers ensure maximum rate of photosynthesis.

  • Spongy Mesophyll Cells: Irregular in shape and distribution,

    situated between palisade cells and lower epidermis, fewer chloroplasts.

    1. Leaves are also the site of *transpiration,*​ ​which is a process by which water evaporates from the leaf and aids the movement of water from the roots to the leaves and cools the plant.
  • The structure of a leaf allows it to carry out these functions in an efficient and effective manner.
  • Sizes and shapes of leaves vary immensely.

  • Plants in hot, dry habitats have:

  • Waxy Cuticles – reduce the amount of water lost through evaporation. - Small Leaves – minimal surface area to reduce water loss.
  • Rainforest Plants have:

  • Large, Thin, Flat Leaves – absorb as much sunlight as possible.

  • Less concern about water loss due to high humidity.

  • Gaseous Exchange:

  • Epidermis covers the surface of leaves.

  • Epidermal cells protect the inner tissues and are able to secrete a waterproof cuticle to prevent evaporation of water.

  • Epidermal cells are transparent to allow light to pass to the cell layers beneath.

  • Guard Cells – control exchange of gases and the loss of water through leaves, occur in pairs surrounding the stoma​.

  • Transport

  • Main transport tissues are the xylem and phloem in the centre of the root

  • The main vein in the leaf, the midrib, and many smaller veins branch out from


  • Distribution of vascular tissue around the plant ensures that all cells are getting the energy required to function.
  • Cellular Respiration in Plants

    1. Plants carry out cellular respiration as well as photosynthesis
  • Occur during night and day

  • Oxygen and CO2 enter and exit the plant via the guard cells

  • Nutrient Requirements in Plants

    1. Carbon Dioxide
  • The opening and closing of the stomata has the greatest effect on carbon dioxide concentration in the leaf.

  • If the stomata is closed, available carbon dioxide is used up and the rate of photosynthesis is reduced.

  • Water
  • Amount of water needed for photosynthesis is small compared to that needed for survival.

  • When water availability level is low, stomata close and reduce the amount of carbon dioxide entering the leaf, reducing the rate of photosynthesis.

  • Light Energy
  • The greater the light intensity the faster the rate of photosynthesis until a plateau is reached.

  • The plateau is where all photosynthesis systems and enzymes are working at optimum rate.

  • Imaging Technologies + Tracing Products Of Photosynthesis
  • MRI→ uses radio waves and magnetic field to take a series of images of the plant structures that are used to produce a 3D image of the structure
  • X-Ray→ Reveals deeper knowledge of the internal structure of the plant
  • Radioisotopes are used to determine whether the oxygen released during photosynthesis originated from the oxygen atom in water or carbon dioxide

  • Carbon-14 is added to the carbon dioxide supply of a plant → The carbon-14 then takes part in the reactions of photosynthesis and is incorporated into the glucose molecules

  • The radioisotopes can be traced by the radiation they emit

  • Gas Exchange in Plants

  • Leaves are adapted for gas exchange.

  • Large and flat – large SAV ratio.

  • Spongy mesophyll layer increases surface area and allow gases to move freely within the leaf.
  • Surface of cell is moist

  • Occurs through stomata and the lenticels.

  • Stomata:

  • Found on the underside of the leaf.

  • Occasionally found on the upper epidermis.

  • Both sides of the stomata are the guard cells.

  • These bean-shaped cells contain chloroplasts (unlike other epidermal cells)
  • The inner wall of each guard cell is thicker than the outer wall.

  • Stomata open and close when the guard cells gain or lose water.

  • Lenticels:

  • Pores through which gaseous exchange happens in woody plants

  • Found on trunks and branches of trees and woody shrubs

  • Appear as small dots, but under the microscope they are seen as clusters of loose cells in the cork layer
  • Diffusion through lenticels is relatively slow

  • Gas Exchange in Animals

  • Oxygen is essential for cellular respiration

  • Carbon Dioxide must be removed as it is highly toxic in large concentrations - Mammals have lungs, fish have gills and insects have tracheal system - Large surface area enhanced by folding, branching or flattening.
  • Moist, thin surfaces so that gasses can dissolve and diffuse.

  • Close proximity to the transport system so gases can move easily.

  • Maintenance of a concentration gradient.

  • Lungs

    1. Gas exchange structures → alveoli
  • Increased surface area – folded

  • Thin lining – flattened single layer of cells

  • Moist surfaces – saturated with water vapour and mucus

  • Shares a membrane with the capillaries, hence this facilitates diffusion of gasses

  • Gills

    1. Gills extract the most oxygen possible out of water
  • As the water passes through the gills oxygen diffuses into the fish

  • This is undertaken by a countercurrent process, this ensures the most oxygen is being diffused from the water (furthest away from equilibrium).

  • Tracheal System

    1. Insects obtain and release air through spiracles
  • Do not have lungs or capillaries

  • Branching air tubes are called tracheal tubes

Oxygen dissolves in fluid, this can be diffused into the cells and carbon dioxide diffuses out.

  • Human Digestive System
  1. Mouth
  • Teeth break down food for more efficient action of enzymes

  • Salivary amylase is release and mixed by the tongue

  • Tongue forms a bolus

  • Oesophagus

  • Peristalsis is the muscular contraction that forces food down

  • Food is moved toward the stomach

  • Stomach

  • Gastric juices contain water, HCL and pepsin

  • Contractions of muscles is a form of mechanical digestion

  • pH → 2.0-3.0

- Breaks down larger and complex proteins to a obtainable level

  • Small Intestine

  • Emulsifies fats into smaller droplets

  • Move by diffusion and osmosis

  • Villi increases the surface area for absorption

  • Lacteals are collected by the lymphatic system

  • Glucose and amino acids are absorbed into the capillaries

  • Liver

  • Duodenum

  • Neutralise the acidic chyme leaving the stomach and break down food

  • Jejunum

  • Breaks down food into smaller pieces

  • Breaks down lipids into fatty acids

  • Ileum

  • Absorption of products are moved by diffusion or active transport through villi

Large intestine

  • Undigested material moves to the large intestine

  • Site of water and salt absorption

  • Remaining faeces is moved to the rectum and anus via peristalsis


Inquiry Question: How does the composition of the transport medium change as it moves around an organism?

  • Transport System in Plants
  • Involves vascular tissue arranged in vascular bundles made up of the phloem and xylem
  • Xylem

  • Moves upwards from the root

  • Movement upwards from the root.

  • Consists of xylem tracheids and xylem vessels.

  • Tracheids: ​long structures with tapered end walls in contact with each other.
  • Xylem vessels are continuous tubes for the transport of water.

- Walls of vessels and tracheids are lined with lignin – helps prevent the collapse of the vessel and easy movement of water.

  • Fibres provide support.

  • Phloem

  • Carries products of photosynthesis - Sieve tube cells and companion cells.

  • Sieve tube cells are long thin phloem cells with large pores through their end cell walls.

  • These perforated cell walls are called sieve plates
  • Sieve tube cells possess mitochondria and endoplasmic reticulum, but no nuclei or other organelles
  • They are arranged end to end forming sieve tubes
  • Sieve tube cells share cytoplasm, their sieve tubes form channels through which sugars and other plant products can flow - Companion cells are found alongside sieve tubes.

  • They have a nucleus and other organelles that are lacking in sieve tubes.

  • Companion cell function is uncertain, but they are thought to assist effectiveness of sieve tube elements by providing ATP.

  • They also help with loading and unloading of sugars into a sieve tube.

  • Transpiration-Cohesion-Tension Theory

    1. Transportation → Process of water vapour leaving the leaves via the stoma
  • Cohesion → Water is attracted to itself as it is a polar molecule: Hydrogen + Oxygen molecules.

Adhesion → Water sticks to the walls of the xylem (Narrow xylem is more beneficial)

  • Positive root pressure in the roots via osmosis

  • Tensions is created by the pull from the leaves

  • Source-Sink Theory

    1. Glucose produced in the leaf during photosynthesis is either stored as starch or converted to sucrose and distributed to all parts of the plant
  • Distribution is called translocation and occurs in the phloem

  • Substances in the phloem move in whichever direction is required. - The phloem also carries amino acids and some mineral nutrients - Sucrose makes up approx. 90% of phloem sap.

  • Once it reaches cells is it converted to glucose for respiration or stored as starch

  • The movement is driven by the formation of high- and low-pressure regions within the phloem

  • Movement occurs from high to low pressure
  • High-pressure occurs where the sucrose is produced (the source) and low-pressure occurs where the sucrose is required (the sink)

  • [The xylem and phloem are adjacent, hence during this process the water] [from the xylem is diffused into the phloem to dilute the sugar.] - Actively transported into stem and root cells for growth.

  • Transport System in Animals

    1. Open circulation
  • Found in invertebrates such as insects

Contains one or more hearts that contract to push blood fluid

  • Hemolymph bathes organs and tissues

  • Blood and interstitial fluid cannot be distinguished

  • Blood is in direct contact with tissue

  • Less efficient, low pressure, Slow

  • Volume of blood cannot be controlled

  • Closed Circulation

  • Found in all vertebrates like fish, mammals frogs and reptiles

  • Contains blood that is enclosed by blood vessels with a driving force of the heart
  • Pathway is from the heart, around the body and back to the heart
  • Transport nutrients and oxygen to the cells as well as returning waste and Carbon Dioxide
  • BLood is not in direct contact with tissue

  • Heart has 4 chambers to divide oxygenated and deoxygenated blood

  • Pumped blood can be controlled by contractions and valves

  • Lymphatic System

  • Transports excess fluid back into the cardiovascular system and is made up of lymph vessels and lymph.
  • Maintains homeostasis

  • Lymph → Watery fluid

  • The Heart

  • Vene Cana → Right Atrium → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary vein → Left Atrium → Left Ventricle → Aorta
  • Composed of cardiac muscle cells

  • Responsible for pumping blood around the body

  • Pulmonary circulation is blood travelling from heart to lungs

  • Systemic Circulation is the process of pumping the blood around the body and back to the heart
  • Structure of Blood Vessels

    1. Each vessel is best structured to suit the function of the vessel
  • Artery

  • Thicker walls and narrow cross section as blood enters under high pressure, and thicker walls minimise the chance of the artery tearing.
  • Walls also are more elastic, so it can expand and contract.

  • Carries blood from the heart.

  • Contraction squeezes blood forward and propels it along.

  • Vein

  • Thinner walls and wider lumen as the blood is not as high pressure.

  • The walls are not as elastic as the veins do not need to contract and expand as much as the arteries.
  • Returns blood to the heart.

  • Cross section is wider to allow easy flow of blood.

  • Blood is propelled by the contracting of muscles surrounding the veins.
  • Valves situated at regular intervals to stop the reverse flow of blood.

  • Capillaries

Walls are one cell layer thick so that substances can be diffused efficiently.

  • Brings blood into close contact with the tissues, enabling exchange of chemical substances between cells and the bloodstream.

  • Red blood cells pass through in a single file, increasing their exposed surface area for the exchange of gases, nutrients and waste.

  • Blood As a Transport Medium

    1. Red Blood cells (Erythrocytes) - Transport oxygen.
  • Form in bone marrow.

  • Haemoglobin (oxygen carrier) is developed within the cell.

  • Round, biconcave and slightly flattened towards the centre – more SA:V and elastic in order to squeeze through capillaries.

  • No nucleus so it has more hemoglobin for oxygen → Structure for function

  • White Blood Cells (Leukocytes) - Also produced in bone marrow.

  • Part of the immune system.

  • Role is to defend the body against foreign bodies.

  • Found in tissues as well as the blood.

  • Can pass through capillaries by squeezing between the cells that make up the wall of the capillary.
  • Larger than red blood cells.

  • Not as abundant as red blood cells.

  • All white blood cells have a nucleus.

  • Platelets (Themocytes)

  • Function in the clotting of blood.

  • Contact between fibres and platelets causes platelets to break open and release an enzyme, thromboplastin, which sets in progress a sequence of steps to seal the blood vessels and cause blood to clot.
  • Crescent shaped.

  • Half the size of red blood cells.

  • Plasma

  • Yellow, watery fluid.

  • 90% water, 10% protein

  • Makes up the majority of the volume of blood and carries many substances throughout the body:
  • Proteins

  • Nutrients

  • Gases

  • Excretory Waste Products

  • Ions

  • Hormones

  • Vitamins

  • Changes in Compositions Of Blood

  • Lungs

As blood moves through the lungs it gains oxygen and loses carbon dioxide.

  • Digestive System

  • Increase in digestive end products.

  • Lymphatic System

  • Gain fatty acids that have been emptied into the bloodstream.

  • Heart

  • High lipid content.

  • Stomach

  • Water and other substances are diffused into the blood.

  • Liver

  • Decrease in digestive end products.

  • Glucose may be added or removed.

  • Urea is added to the blood.

  • Toxins such as alcohol are removed.

  • Some vitamins and iron are removed.

  • Kidneys

  • Urea is decreased.

  • Excess water and salts are removed.

  • Large Intestines

  • Water, salts and vitamins are absorbed into the blood.

  • Endocrine Glands - Hormones are added.

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