Organisation Of Living Things Notes

Organisation of Cells

  • Inquiry Question: How are cells organised in a multicellular organism?

Types of Organisms

  • Organisms can exist as:
    • Unicellular (single cell)
    • Colonial (single cells working together)
    • Multicellular (many cells)
  • All are composed of cells.
Unicellular Organisms
  • Made of one independent cell.
  • Can be prokaryotic (bacteria) or eukaryotic (paramecium).
  • The single cell performs all survival and reproduction functions:
    • Nutrient obtainment
    • Gas exchange
    • Waste removal
    • Reproduction
  • Small size due to all metabolic processes occurring in one cell.
  • High surface-area-to-volume ratio (SA:V) for efficient material exchange.
Colonial Organisms
  • A group of identical single-celled organisms (colony).
  • Each cell can perform all life functions.
  • Some have cells with specialised functions coordinated within the colony.
  • Examples: Volvox, coral, jellyfish.
  • Volvox: composed of over 500 algae cells.
Multicellular Organisms
  • Made of many different types of specialised cells.
  • Similar cells group together for specialised functions.
  • Specialised cells cannot live independently.
  • Embryonic (young) cells differentiate into specialised cells.
  • Larger in size, smaller total SA:V.
  • Both passive and active transport are used for material exchange.
Advantages of Multicellularity
  • Energy-efficient cell specialisation.
  • Longer lifespans.
  • Increased genetic diversity (sexual reproduction).
  • Adaptability to changing environments due to genetic diversity.
  • Less vulnerability to short-term environmental changes.
  • Increased size and mobility.
  • More complex functions.
Disadvantages of Multicellularity
  • More energy is required for survival and reproduction.
  • Cells are dependent on each other.
  • Slower population evolution and adaptation.
Comparison of Organism Types
  • Unicellular:
    • Cells perform all survival tasks.
    • Asexual reproduction (binary fission, budding).
    • Specialised structures for movement and food capture.
  • Colonial:
    • Cells have some specialisation and cooperation.
    • Sexual reproduction is possible.
    • Specialised cells for filter feeding, stinging, or mutualistic relationships.
  • Multicellular:
    • Highly specialised and differentiated cells.
    • Cells depend on other cells, tissues, and organs for survival.
    • Sexual reproduction is common.
Colonial Flagellate Hypothesis
  • Unicellular organisms aggregated to form a colony.
  • Cells in the colony could initially survive if separated.
  • Over time, cells differentiated and became dependent on each other, forming multicellular organisms.
Key Concepts
  • Unicellular organisms:
    • One cell carries out all metabolic processes.
    • Can be prokaryotic or eukaryotic.
    • High SA:V for efficient substance exchange.
  • Colonial organisms:
    • Evolutionary link between unicellular and multicellular organisms.
    • Individual cells living together.
    • All cells capable of metabolic functions.
    • May have simple specialised cells.
    • Examples: Volvox and choanoflagellates.
  • Multicellular organisms:
    • Many different types of specialised cells.
    • Similar cells grouped together for specific functions.
    • Individual cells cannot live independently.

Cell Specialisation

  • Multicellular organisms divide labour among cells for efficiency.
  • Cells differentiate into special roles.
  • When fertilisation occurs, cells rapidly divide as undifferentiated cells.
  • Genes are turned on to make cells differentiated as the organism develops.
Cell Differentiation
  • Specialised cells work together in multicellular organisms.
  • All specialised cells originate from stem cells, which differentiate into specialised cells.
  • Examples:
    • Red blood cells: gas delivery (no nucleus, biconcave shape for high SA:V)
    • White blood cells: immune defense
    • Neurons: brain & nerve
    • Gametes: reproduction
  • Stem cells: embryonic (from zygote) or adult (from bone marrow).
  • In plants, specialised cells form by differentiation of meristematic tissues.
Red Blood Cells
  • No nucleus and lack organelles for haemoglobin to bind and carry oxygen.
  • Small size and biconcave shape increase SA:V, allowing rapid oxygen diffusion.
  • Small size allows squeezing through capillaries.
Palisade Cells in Plants
  • Found in leaves where photosynthesis occurs.
  • Elongated shape maximises SA:V, allowing efficient exchange of substances.
Advantage of Cell Specialisation
  • Cells are more efficient with one function.
  • Multicellular organisms are more energy-efficient than unicellular organisms.
Cell Specialisation and Gene Expression
  • All cells with a nucleus contain the same genetic material (DNA).
  • Gene expression builds different cell structures depending on the specialised cell's function.
Cell Structure and Function
  • Specialised cells have particular structures for particular functions.
  • Structural features ensure optimal cell function.

Autotrophs and Heterotrophs

Autotrophs
  • Make their own organic compounds from inorganic matter and energy (carbon fixation).
  • Also called producers.
  • Use sunlight as an energy source to convert inorganic matter into organic matter.
Heterotrophs
  • Cannot carry out carbon fixation.
  • Obtain organic compounds by consuming other organisms or their products.
  • Called consumers in the ecosystem.
Gas Exchange in Autotrophs
  • Plants have an optimal temperature range for photosynthesis (enzymes such as RuBisCO can denature if it gets too hot).
Complex vs Simple Plants
  • Complex (vascular) plants:
    • Specialised tissues for transporting water and nutrients (e.g., flowering plants).
    • Vascular plants have two systems: root and shoot.
  • Simple (non-vascular) plants:
    • Simplified tissues to absorb water directly (e.g., mosses and some algae).
    • Limited size due to limited water transport.
Systems in Complex Plants
  • Root system: supports the plant and absorbs water and nutrients.
  • Shoot system:
    • Vegetative parts: leaves and stems.
    • Reproductive parts: flowers and fruits.
Structure of a Leaf
  • Site of photosynthesis.
  • Contains cells with chloroplasts and a thick cell wall.
  • Epidermis: outer layer for gas exchange.
    • Thickness varies depending on the plant and its environment.
  • Stomata: pores within the epidermis that regulate gas exchange.
    • Open and close with guard cells.
  • Cuticle: waxy layer that protects from excessive water or gas exchange loss.
Leaf Structure Components
  • Upper and lower epidermis (cuticles)
  • Mesophyll
  • Guard cells
  • Waxy cuticle:
    • Thin layers on leaf surfaces.
    • No chloroplasts.
    • Repel water, reducing water loss.
  • Mesophyll:
    • Main photosynthetic cells.
    • Palisade and spongy mesophyll.
  • Palisade mesophyll:
    • Elongated cells dense with chloroplasts.
    • Close to the upper epidermis.
    • Responsible for the majority of photosynthesis.
  • Spongy mesophyll:
    • Between palisade mesophyll cells and lower epidermis.
    • Fewer chloroplasts than palisade
    • Irregular shape and distribution for air movement.
  • Guard Cells and Stomata
    • Stoma is the opening to an air space in the lower epidermis.
    • Guard cells surround a pore, creating an opening through the epidermis and cuticle.
    • Gas exchange in shoots occurs through stomata and lenticels.
    • When guard cells are filled with water, they become turgid, and bend outwards to open the stoma, allowing for gas exchange.
    • When water is lost from the guard cells they become flaccid, and stomata close, preventing both gas exchange and water loss.
    • Plants have to balance their requirement for gas exchange and the necessity for water conservation.
    • Stomata open in light and close in the dark.
  • Lenticels
    • Pores through which gaseous exchange occurs in woody parts of plants.
    • Clusters of loose cells in the cork layer of bark.
    • Diffusion of gases is relatively slow.
  • Vascular plants include ferns, cycads and flowering plants.
  • Vascular plants include:
    • Xylem: Transports water and inorganic nutrient absorbed from the soil up the plant
    • Phloem: Transports dissolved sugars produced by photosynthesis from the leaves throughout the plant and organic substances such as amino acids.
  • Plant tissue is also organised into organs. Two of the major organs in plants are leaves and roots.
Root System
  • Main functions are to anchor the plant and absorb water and mineral ions.
  • A large surface area is required for efficient absorption.
  • Branching root systems increase the surface area.
  • Large root systems of many trees in nutrient- poor rainforest soils do not penetrate deep into the soil layers and instead grow above ground.
  • Root Hair Cells
    • This large surface area is achieved with flattened epidermal cells that possess fine extensions called root hairs.
    • Root hairs increase surface area and maximise water and mineral uptake.
    • Water and Mineral Movement
      • Water moves from the soil into the root by osmosis.
      • Mineral ions usually move into the root by diffusion, but if the concentration gradient is too low they are moved in by facilitated diffusion or active transport.
      • Root cells do not contain chloroplasts and do not photosynthesise but, as with all living cells, they carry out aerobic cellular respiration.
      • Oxygen gas diffuses into the root cells and carbon dioxide gas diffuses out during respiration.
  • Transport system in Plants
    • Plants have a transport system to move things around.
    • The xylem moves water and solutes, from the roots to the leaves in a process known as transpiration.
    • The phloem moves glucose and amino acids from the leaves all around the plant, in a process known as translocation.
    • The xylem and phloem are arranged in groups called vascular bundles. The arrangement is slightly different in the roots to the stems. The xylem are made up of dead cells, whereas the phloem is made up of living cells.
  • Both the xylem and the phloem is made up of rows of cells that form a continuous tube, running the whole length of the plant.
  • The xylem vessels are made of elongated dead cells that are impermeable (does not allow fluid to pass through) to water and have walls containing lignin (woody material). Because of this, the xylem is tough, which is why the vascular bundles in the roots are in the centre. They prevent the plant from being pulled out of the ground. They are also more protected in the centre, where the stem needs to be protected from being squashed which is why the vascular bundle in near the edge to provide strength and support.
  • The phloem vessels are made up of living cells. They transport sucrose and amino acids up and down the plant depending on where it is needed. Whereas in the xylem it is one way which is from the roots to the leaves
  • Transpiration “The evaporation of water from the aerial part of a plant” -> so the leaves and stems So, by water evaporating out of these parts mostly the leaves a suction pressure is related which draws up the water through the plant → this is called the transpiration pull
  • While Transpiration is Happening
    • Water passes in from the soil by osmosis, passing down the concentration gradient, and into the root hair cell’s cytoplasm, and then on to the xylem vessels.
    • Transpiration at the leaf causes a transpiration pull.
    • Because water molecules are cohesive, water is pulled up through the plant in the transpiration stream.
    • The leaf cells need water for photosynthesis, and water also keeps the cells turgid, which supports the plant.
    • Inside the leaves, water is drawn out of the xylem cells to replace the water lost through transpiration.
    • The cohesive nature of water also pulls the water through the plant. As water leaves the xylem and moves into the leaf, it pulls more water molecules behind it.
    • The transpiration stream not only involves water but also transports mineral ions dissolved in the water from the roots to the leaves.
    • The transpiration rate varies due to different factors. Environmental factors like temperature, humidity, wind, and light intensity affect the rate, as well as physical factors such as the presence of a waxy cuticle, the number of stomata, the nature of the guard cells, the size of the leaf surface area, and whether the leaf is folded or flat.
  • If the rate of transpiration increases, the rate of water absorption by the roots needs to increase too. When water is scarce or if the roots are damaged, the plant reduces its transpiration rate by closing some of the stomata. Guard cells on either side of the stomata regulate this process. During daylight hours, chloroplasts produce sugar, which lowers the water potential of the guard cells, causing them to take in water by osmosis. This makes the guard cells turgid, and because they have different cell wall thicknesses, they bend more on the outside into sausage shapes, opening the stomata and allowing water to be lost.
  • At night, the sugar produced by the chloroplasts gets used up, increasing the water potential of the guard cells. With more water and less sugar, the guard cells lose water by osmosis and become flaccid, causing the stomata to close and reducing water loss. So, water moves through the plant up the xylem, pulled along the transpiration stream by the transpiration pull. The plant controls water loss by closing the stomata based on how flaccid or turgid the guard cells are. In the final part of this video, we will look at the movement of glucose, because water is important, but so is food.
  • Translocation Sugars move up and down the plant in the phloem. The phloem uses active transport to transport the food nutrients like glucose and amino acids around the plant. Glucose is made in the leaves by photosynthesis. Glucose is converted into sucrose in the leaves, which then enters the phloem vessels, as do amino acids. They then need to be transported around the plant to every single cell. The areas of the plant where sucrose is made are called the sources, and where they are delivered are called sinks. The phloem uses active transport because the sucrose moves against its concentration gradient from a lower concentration, where it is made, to a higher concentration in the phloem cells.
  • Cohesion Adhesion Theory
  • When a plant closes its stomata, it can no longer exchange oxygen and carbon dioxide, therefore the rate of photosynthesis decreases. Outline the benefit of closing the stomata. Define the terms turgid and flaccid. Looking at the graph below, Identify the overall effect of increased carbon dioxide levels on the rate of photosynthesis? If a plant is given unlimited carbon dioxide and unlimited access to light, will photosynthesis increase? Explain your answer.
  • Closing stomata helps prevent water loss through transpiration, especially in dry or hot conditions, thus conserving water within the plant. This adaptation is crucial for maintaining proper hydration and preventing wilting, particularly in environments with limited water availability. While closing stomata reduces the rate of photosynthesis due to decreased carbon dioxide intake, the water-saving benefits outweigh this temporary reduction, ensuring the plant's survival.
  • Regarding the graph, increased carbon dioxide levels generally lead to higher rates of photosynthesis, as carbon dioxide is a key reactant in the photosynthetic process. The graph likely shows a positive correlation between carbon dioxide concentration and the rate of photosynthesis until a certain threshold is reached, beyond which further increases in carbon dioxide may have diminishing returns due to other limiting factors such as light intensity or temperature
  • If a plant is given unlimited carbon dioxide and unlimited access to light, photosynthesis will increase initially due to the availability of more carbon dioxide, which is a crucial component in the photosynthetic process. However, after reaching a certain point, other factors such as light intensity, temperature, or availability of other nutrients like water or minerals may become limiting factors. Therefore, while unlimited carbon dioxide can enhance photosynthesis up to a certain extent, other environmental factors also play significant roles in determining the maximum rate of photosynthesis achievable by a plant.
  • Imaging Technologies and Photosynthesis
    • Radioisotopes are forms of an element that emit radiation, which can be detected by a number of means. They act as tracers and are used to follow the pathways of molecules involved in photosynthesis.
    • Radioisotopes were used to determine that oxygen produced in photosynthesis came from the water molecule and not the molecule of carbon dioxide.
    • Carbon-14 added to the carbon dioxide supply traced the movement of the glucose produced through the plant.
    • New technologies can be used to produce 3D images of the structures and pathways involved in the movement of products of photosynthesis.
  • THEORIES ABOUT XYLEM AND PHLOEM
    • Experimental evidence has shown the type of materials that move through xylem and phloem in plant stems and the directions in which they move, but the explanation of how this movement occurs in each is presented as a theory. Remember a theory is a scientist’s explanation of a phenomenon, based on observation.
    • THE TRANSPIRATION STREAM THEORY
    • The transpiration stream in xylem occurs due to physical forces that result from water (and ions) being moved by passive transport.
      • A column of water is sucked up the stem by the evaporative pull of transpiration and is known as the transpiration stream.
      • The movement of this column of water from the roots is aided by a number of other factors:
      • The cohesion of water molecules to each other. These cohesive forces arise from the fact that water molecules are polar. This means that one end of the molecule has a slightly negative charge while the other end has a slightly positive charge. This causes the water molecules to stick together with the positive and negative ends attracted to each other. This forms a continuous stream of water so that when molecules of water are drawn up the xylem other water molecules move with them.
      • Adhesive forces between the water molecules and the walls of the xylem vessel cause the water to rise up the sides. The narrower the vessel, the higher the water will rise up. The combined forces of adhesion and cohesion ensure the continuous column of water moves through the xylem tissue in the stem of the plant.
      • The narrow thickened walls of the xylem vessel can withstand the tension created in the water column and offers little resistance to the flow of water.
      • Once water has been absorbed into the roots of the plant (by osmosis) along with mineral ions (by diffusion and active transport), these substances move across the root into the xylem. A small amount of root pressure results from the continual influx of more water and ions, forcing the solution already present to move upwards. This pressure is
    • THE TRANSPIRATION STREAM THEORY
      • Once the water has been absorbed into the roots of plants (by osmosis) along with mineral ions (by diffusion and active transport), these substances move across the root into the xylem. A small amount of root pressure results from the continual influx of more water and ions, forcing the solution already present in the xylem upwards.
      • Most of the upward movement in xylem seems to be as a result of the transpiration stream – water is drawn up the xylem tubes to replace the loss of water from the leaves by transpiration. This is based on evidence gathered by biologists.
    • Evidence
      • Xylem vessels are hollow and narrow, offering very little resistance to the flow of water
      • The physical properties of water contribute to the formation of a continuous stream.
        • Adhesive forces lead to capillarity (water rises up the bore of xylem) and cohesive forces (the attraction of water molecules to each other) which ensure that a continuous column of water that moves upwards is maintained in the xylem vessels.
      • A concentration gradient exists across the leaf: At the surface of the leaf, the osmotic pressure is high (water concentration is low) because water is continually being lost by evaporation through the stomata (transpiration). In the centre of the leaf the osmotic pressure is low (water concentration is high).
  • Source to Sink or Pressure Flow theory
    • Sources:
      • Definition: Sources are the parts of the plant where sugars are produced or stored. These are typically leaves (through photosynthesis) or storage organs like roots and tubers.
      • Process: In the leaves, sugars are produced via photosynthesis. In storage organs, sugars can be mobilised and released into the phloem.
  • Sinks: * Definition: Sinks are the parts of the plant that consume or store the sugars. These can include roots, developing fruits, seeds, and growing parts of the plant like young leaves and shoots. * Process: These parts require energy and building materials, so they draw sugars from the phloem.
    • Glucose is organic as it contains carbon atoms within it
    • The phloem is hence responsible for transporting organic substances to all cells → All cells require sugar to respire
    • Theories about Xylem and Phloem
      • The theories of how movement of substances occurs in plants have been tested by examining whether their consequences (predictions) are borne out by observation and experimentation.
      • They have modified over time, but the current most commonly accepted theories are:
        • The transpiration stream theory (cohesion-adhesion-tension theory) of movement of water and mineral ions in xylem
        • The pressure flow theory (source-path-sink theory) of translocation of organic nutrients in phloem.
  • Cell discovery timeline
    • Parts of the cell
      • Membrane
      • Nucleus
      • Golgi
      • Mitochondria
  • Theories About Xylem and Phloem
    • Transpiration And Translocation
    • Plant Anatomy
    • Plant Physiology
    • Scientific Progress in Photosynthesis
  • Vascular systems and Photosynthesis.

Heterotrophs

  • TRANSPORT SYSTEMS IN ANIMALS
    • Anatomy is widely varied throughout the animal kingdom, including the methods by which nutrients and gases are transported to cells.
      • There are two types of transport systems:
        • Firstly, a closed circulatory system uses blood vessels to transport nutrients to cells, with blood being pumped around the system by the heart. Exchange of nutrients from the blood into cells happens when the blood flows into vessels with very thin walls, where nutrients are able to move in and out through diffusion. The enables the organism to have more control over blood flow.
        • Secondly an open circulatory system is one where blood flows freely around the body, with blood surrounding tissues (kind of like soaking a sponge, where the cells are the sponge), and oxygen flows directly to the cells from the respiratory tract. It’s kind of like giving the tissues a bath in dissolved nutrients and gases. Arthropods (invertebrates with exoskeletons such as insects) have an open circulatory system.
  • CIRCULATORY SYSTEM: MAMMALS
    • The circulatory system is the organ system found in mammals that is responsible for the circulation of blood around the body. This is essential for the transportation of nutrients, gases, hormones, and blood cells to tissues around the body. This helps to produce molecules for life, stabilise the body, and fight infection.
    • The main organs of the circulatory system are the heart, lungs, arteries, veins and capillaries.
    • Oxygenated blood is pumped from the heart to the cells of the body. Deoxygenated blood is delivered back to the heart, pumped to the lungs and then back out to the cells.
    • Mammals have a double cycle circulatory system. This simply means that the heart pumps blood to the lungs and then it is passed back to the heart, before being pumped to the rest of the body. There are two loops of blood flow connected to the heart. This is facilitated by the heart having four chambers, two on the left which pump the blood to the lungs, and two on the right to pump the blood to the capillaries.
    • Arteries: Arteries are the vessels responsible for transporting oxygenated blood from the heart to the tissues. Due to this function they have thick elastic walls which can withstand a high degree of pressure, with a thick lining of muscular tissue surrounding a small lumen (intra-vessel space). This helps to control the flow of blood to the tissues.
    • Veins: Veins are the vessels responsible for transporting deoxygenated blood from the tissues back to the heart. As blood flows back to the heart at a much lower pressure the veins have thin walls and a large lumen to allow a large amount of blood through. Additionally, they have specialised valves which prevent back flow at low pressures.
    • Capillaries: Capillaries are the direct interface between blood and cells. They provide a surface for exchange of substances into and out of the cells. To perform this function, they have very thin walls, only one cell thick, and a tiny diameter which can only fit one blood cell through at a time. This enables fluids and gases to be easily moved through capillary walls.
    • Blood: Blood is the fluid medium used in animals to transport nutrients, gases and water in cells. It is also used to remove metabolic wastes from cells.
    • SUBSTANCES TRANSPORTED IN BLOOD
    • Substances are transported in a number of different ways in blood:
      • Carbon Dioxide is transported in three different ways: dissolved directly into the plasma, bound to haemoglobin, or as a bicarbonate molecule.
      • Oxygen is transported bound to haemoglobin as oxyhaemoglobin.
      • Water is transported in plasma.
      • Lipids are transported bound to proteins as lipoproteins.
      • Nitrogenous wastes are transported as Urea in the plasma.

CIRCULATORY SYSTEM: FISH

  • Fish have a single circuity of blood flow. This means that the blood if pumped to the gills and then flows straight to the capillaries without passing back through the heart. Unlike the mammalian heart, which has a double cycle circulatory system, the hearts of fish only have two chambers, as it does not need to regulate a second circuit of blood flow. Instead of pumping blood to the lungs, fish hearts pump blood to their gills, where gas exchange occurs.
  • Open Circulatory System
    • Insects
    • The open circulatory system requires less energy for distribution. This system is more suited to animals that have a slower metabolism and a smaller body.
    • Due to the absence of arteries, blood pressure remains low, and oxygen takes longer to reach the body cells making it only feasible in small animals.
      • If an organism has a low metabolism, it is less active.
    • WHY DO YOU THINK, MULTICELLULAR ORGANISMS NEED EFFICIENT TRANSPORT SYSTEMS?
    • Mammalian Digestive System
      • Heterotrophs are living things that need to take in ot ‘eat’ all their nutrient requirements to supply energy and the building blocks for organic compounds.
      • Complex foods are eaten or ingested and broken down by our digestive system in simpler molecules which can be absorbed into our bloodstream
        • Digestion: the breakdown of food into small water-soluble molecule that can be used by the cell in metabolic processes.
        • Mechanical Digestion: The process of digestion begins in the mouth. Food is broken down into smaller pieces by chewing (mastication), mechanical digestion. Saliva in the mouth contains an amylase enzyme which begin to break down food leaving starch molecules. Food travels from the mouth, down the oesophagus, and into the stomach.
        • Chemical Digestion: In the stomach, gastric juices begin to break down proteins in food. Hydrochloric Acid and pepsin break down proteins into peptides. Digestion in the stomach continues for about 1-2 hours in humans, before moving into the duodenum
        • HOW ARE PROTEINS, LIPIDS AND CARBOHYDRATES BROKEN DOWN
        • Protein digestion: proteins are broken down into peptides, and then into amino acids which are absorbed into the blood. This is performed by proteolytic enzymes produced in the pancreas.
        • Lipid digestion: lipids, also called fats are broken down into glycerol and fatty acids.
        • Carbohydrate digestion: carbohydrates are broken down into simple sugars (monosaccharides) by enzymes, including pancreatic amylase and glucoamylase
        • 95% of the absorption of nutrients occurs in the small intestine.
        • SMALL INTESTINE
          • The small intestine lining is composed of epithelial cells (or enterocytes), which are folded, and form finger-like projections called villi
          • In the epithelial cell thare are individual projections called microvilli. These structures increase the surface area of the intestinal lining, allowing for increased absorption. Nutrients and minerals diffuse across the cell membranes into the cell. Within the villi there is a network of capillaries and lymphatic vessels. The epithelial cells will transport amino acids and carbohydrates into the blood vessels, and lipids into the lymphatic vessels. Water is also absorption by this process in the small intestine.
          • LARGE INTESTINE
            • Elimination of solid waste: after water as been reabsorbed in the large intestine, excess water is moved through the colon by muscular contractions. This semi-solid waste is then moved to and stored in the rectum.