Organisation Of Cells
Inquiry Question- How are cells arranged in a multicellular organism?
Unicellular Organisms (Bacteria)
- 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)
- 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.
- 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
FORMATION OF SPECIALISED CELLS
- 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.
- Organelle Cell Tissue Organ Organ System Organism
- Mitochondria Cardiac Muscle Cell Cardiac Muscle Tissue Heart Cardiovascular System Human
- 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.
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)
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 cells are highly specialized for contraction
Skeletal, Smooth, Cardiac
- Responsible for the movement of the body and particular contractions in various processes (oesophagus peristalsis)
- Meristematic Tissue
Tips of roots and shoots
Cells divide to produce new growth
Site of cell differentiation
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
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
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?
- 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)
- Obtain organic compounds from obtaining other organism
Include all animals and fungi
Vascular and Nonvascular Plants
- 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.
- 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)
- 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)
- 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.
- 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.
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.
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
- 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
- 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.
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.
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.
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.
- 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 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).
- 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
Teeth break down food for more efficient action of enzymes
Salivary amylase is release and mixed by the tongue
Tongue forms a bolus
Peristalsis is the muscular contraction that forces food down
Food is moved toward the 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
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
Neutralise the acidic chyme leaving the stomach and break down food
Breaks down food into smaller pieces
Breaks down lipids into fatty acids
Absorption of products are moved by diffusion or active transport through villi
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
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.
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.
- 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
- 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
- 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
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
- Transports excess fluid back into the cardiovascular system and is made up of lymph vessels and lymph.
Lymph → Watery fluid
- 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
- Each vessel is best structured to suit the function of the vessel
- 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.
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.
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
- 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.
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.
Half the size of red blood cells.
Yellow, watery fluid.
90% water, 10% protein
- Makes up the majority of the volume of blood and carries many substances throughout the body:
Excretory Waste Products
Changes in Compositions Of Blood
As blood moves through the lungs it gains oxygen and loses carbon dioxide.
Increase in digestive end products.
Gain fatty acids that have been emptied into the bloodstream.
High lipid content.
Water and other substances are diffused into the blood.
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.
Urea is decreased.
Excess water and salts are removed.
Water, salts and vitamins are absorbed into the blood.
Endocrine Glands - Hormones are added.