Multicellular Organisms upto 3.3

🪷3.1: Specific cell structure and functions develop through cell differentiation.

🪻Recognise that:

Cells in a multicellular organism are genetically identical.

All cells in organisms contain the same genome → gene expression leads to specialisation.

Multicellular organisms composed of many different cell types, each with specialised structures and functions determined by its genetic material stored in one or more chromosomes.

Gene expression is responsible for cell specialisation.

Chromosomes: contain hundreds of genes and encode the production of protein molecules that give cells specialised structure and function.

Genes switched on and off in response to signals from external/internal environment.

Switched on gene = expressed, protein for it is synthesised

Switched off gene = not expressed

Specialised cells: maintain a specific gene expression program to perform their distinct roles. Therefore, there is a difference in cell types due to… differential gene expression.

Cell differentiation: Process of development where cells become specialised through highly regulated gene expression. EX: INS gene that encodes protein insulin exclusively expressed in beta cells (animal pancreas), making them specialised (highly differentiated) insulin secreting cells.

🦋Differentiated cells: A cell with specific structure and function arising from its unique gene expression pattern. EX: Human epithelial cells (express ⅓ of its genome).

Highly differentiated cells: Express very small fraction of their genes. EX: muscle and nerve cells.

🦋TSHR is expressed from a gene present in all nucleated cells. Why is TSHR only found in thyroid follicular cells?...TSHR is only expressed in thyroid follicular cells.

🦋Describe development of magenta and yellow coloured cells from stem cells…

Stem cells respond to chemical factors in their environment that trigger a unique pattern of gene expression. Different proteins are expressed, resulting in cells with different structure and functions.

🦋STEM cell: unspecialised/undifferentiated cell capable of mitosis, can differentiate into one or more specialised cell types. Found in developing embryo’s, bone marrow, fatty (adipose) tissue, the brain, skin, and blood vessels.

Most differentiated cells arise from STEM cells that developed into differentiated cells through differential gene expression. 🦋EX: animal skeletal muscle cells. STEM cells respond to signals that trigger the expansion of gene myoD → turns on genes encoding muscle proteins, turns off genes encoding cell division → stem cell becomes differentiated skeletal muscle cells with different gene expression patterns.

🪷3.2 Multicellular organisms have a hierarchical structural organisation of cells, tissues, organs, and systems.

Organ systems in a multicellular organism are interdependent and function together to ensure the survival of the organism.

🪻Illustrate the relationship between the structure and function of cells, tissues, organs, and/or systems.

Lifestyle choices affect the functioning of organs and systems.

Lifestyle choice: persons decision about living and behaving depending on individuals values, preferences and attitude.

Diet, level of exercise, amount of sleep, use of drugs including painkillers, cigarettes, alcohol.
Affect functioning of individual’s organs and systems, both positive and negative effects.
Idk if i need more yet

🪻Use examples from plants and animals to explain the organisation of cells into tissues, tissues into organs, organs into systems.

4 Levels of organisation:

Cell: Basic unit of structure and function in living things. Multicellular organisms composed of specialised cells that perform specific functions.

Tissue: Groups of cells that are similar in structure and function work together to perform a specific function.

Ex: animals → muscle tissue → responsible for movement.
Adult vertebrate animals → 4 kinds of tissues: epithelial, connective, muscle, nerve.

Epithelial Tissue (Epithelium):

Covers every surface of vertebrate body
Functions: barrier protection, secretion, absorption
4 types of epithelium: simple, stratified, pseudostratified, glandular. Each contain free surface specialised for protection, secretion, absorption. Diff epithelium types = epithelial cells w/ diff structure and function.
Different epithelial cell types facilitate 1/+ functions: squamous, cuboidal, columnar.

Simple epithelial tissue: Single layer of cells specialised for absorption.

Ex: simple squamous epithelium: lines blood vessels, alveoli → single layer of flattened cells increases diffusion rate of nutrients, respiratory gases, wastes.
Ex: simple columnar epithelium: lines digestive tract → single layer of rectangular cells specialised for nutrient absorption.
Ex: simple cuboidal epithelium: lines kidney tubules → single layer of cube shaped cells specialised for reabsorbing nutrients from blood.

Stratified epithelial tissue: Multiple layers of flattened cells specialised for protection against abrasion, infection and drying out.

Stratified squamous epithelium: outer surface of skin, lines mouth, oesophagus, vagina.
Stratified cuboidal epithelium: mammary gland duct, sweat glands, salivary glands.

Connective Tissue: stabilise, bind, support other tissues.

Vertebrate animals have various kinds of connective tissue: loose connective, adipose, fibrous connective (tendons/ligaments), cartilage, bone, blood.

Loose connective tissue: beneath most epithelial layers, between muscles, binds and supports organs.

Contains fibroblasts: cells that produce & secrete large molecules (carbohydrates and protein fibres that bind cells).

Collagenous fibres: provide strength, flexibility.
Elastic fibres: stretch and snap back to og length.
Reticular fibres: join connective tissue to adjacent tissues.

Adipose tissue: under skin & surrounding organs, energy storage, insulation, cushioning organs.

Contains adipocytes: cells that store fats, molecules that store energy and provide thermal insulation.

Fibrous connective tissue: strong fibres attaching muscle to bone (tendon), bone to bone (ligament).

Cartilage: strong, flexible, nose, outer ribs, ears, joints, b/w vertebrae in backbone, cushions bone, protects from impact.

Chondrocytes: cells suspended in fluid → allows joints to move.

Bone: Rigid connective tissue, composed of minerals, protein fibres, protects and supports internal structures, facilitates movement, produces blood cells.

Oestocytes: Cells that store nutrients and secrete materials to form hard skeleton.

Blood: tissue found throughout body, contains RBC’s, transport nutrients, wastes, respiratory gases, WBC’s fight infection, platelets form blood clots.

Muscle Tissues: made up of specialised cells that facilitate movement.

3 types: skeletal, cardiac, smooth.

Skeletal muscles: attached to bones by tendons, contraction → bones move at joints.

Muscle fibres: very long muscle cells with multiple nuclei.

Cardiac Muscle: heart walls, involuntary contractions that pump blood through circulatory system.

Small interconnected cells, single nucleus, interconnections permit movement of materials b/w cells.

Smooth muscle: walls of hollow internal organs eg. intestines and tubes eg. blood vessels, involuntary movements e.g contractions in digestive system → moves food along.

Sheets of spindle-shaped cells, single nucleus.

Nervous Tissue: makes up brain, spinal cord, nerves, composed of neurons and glia

Specialised cells that conduct messages thru body,
Neurons: transmit nerve impulses (electrochemical signals) around body, coordinate various life processes of MRSGRENHE.
Glia: nourish, insulate, replenish neurons, eliminate foreign materials in and around neurons.

Plant tissue: Vascular plants = 3 types of tissue → dermal, vascular, ground, form continuous throughout plant.

Dermal tissue: Outer covering, protects plants from disease and water loss.

Nonwoody plants: single layer of tightly packed cells (epidermis).
Woody plants: epidermis of older regions of stems/roots replaced by periderm

Epidermis has specialised function in addition to protection from disease and water loss in each organ.

Leaves and most stems: Produces cuticle (waxy epidermal coating) to prevent water loss.
Leaves and some stems: guard cells, facilitate gas exchange.
Epidermal outgrowth: trichomes, reduce water loss, reflect excess sunlight, secret fluids and toxic substances defend against herbivores.
Root hairs: absorbs minerals and water from the soil, increase SA:V ratio, to exchange water, mineral and waste with soil.

Vascular Tissue:

2 primary functions: transport of materials throughout plant, mechanical support.
2 types: xylem, phloem
Xylem: transports. water, dissolved minerals upwards → roots to stems/leaves. Hollow, elongated, porous cells
Phloem: transports sugar to where it is needed/stored →

Ground Tissue: Neither dermal nor vascular. Cells specialised for storage, photosynthesis, support, short-distance transport. Ex: in leaves, specialised cells with shapes and chloroplasts that maximise light absorption in photosynthesis.

Organ: body structures composed of different tissues that work together to perform specific functions.

Vertebrate organs composed of epithelial, connective, muscle and nervous tissues. Ex: Stomach → Epithelial tissue secretes acid to digest food → nervous tissue stimulates cells to release the acid → smooth muscle tissue contracts to push food thru stomach → connective tissue supports other tissues by supplying nutrients, removing waste.

Organs of vascular plant: Contain dermal, vascular and ground tissues.

Roots: anchors vascular plant to soil, absorbs water and nutrients from soil, stores nutrients.
Stems: Elongated organ, erects/orients leaves to maximise photosynthesis, elevates reproductive structures to facilitate pollen and fruit dispersal. Green stems = limited amt of photosynthesis.
Leaves: Primary photosynthetic organ, absorbs light, exchanges gases with atmosphere, dissipate heat, defend themselves from pathogens, herbivores.

Ex: Leaves

Dermal tissue prevents water loss, facilitates gas exchange → ground tissue absorbs sunlight, facilitates photosynthesis → vascular tissue supplies water for photosynthesis, transports sugars from leaves to stems and roots. All tissues assembled into a single organ that facilitates common function of photosynthesis.

Organ Systems: Group of organs that cooperate to facilitate bodily functions.

Vertebrate: 11 principal organ systems. Ex: Circulatory system: heart, blood vessels, cooperate in transporting blood, nutrients, respiratory gases, wastes around body.
Organ systems in plants and animals r interdependent. Ex: Digestive and circulatory system: Digestive system breaks down food into soluble compounds, absorbed into blood stream from intestines → Circulatory system, blood vehicles nutrients to tissue cells for respiration.

Vascular plants: 2 organ systems, root and shoot, interdependent.

Root: All organs below surface.
Shoot: All organs above surface.
Roots need energy to diffuse minerals against concentration gradient in soil, acquired from carbohydrates in respiration → rely on carbohydrates produced in photosynthesis in the shoot system.
Shoot system requires water and nutrients for photosynthesis → cannot access without root system.

🪷3.3 Multicellular organisms exchange materials with their environment…

Exchange surfaces in an organism must be thin, moist, and have a large surface area. In many animals, a rich blood supply is also essential.

Gas exchange in animals: uptake of oxygen, discharge of carbon dioxide.

Respiratory surfaces tend to be large and thin:

Moist: gases must dissolve in water to diffuse in and out of cells.
Thinness: Increases diffusion rate by shortening diffusion path b/w respiratory cells and blood.
Large surface area: diffusion rate increases with surface area of exchange surface.
Rich Blood Supply: blood carries oxygen away, carbon dioxide in → maintains steep concentration gradient so diffusion keeps going instead of reaching equilibrium.
Ventilation: Breathing continually replaces air in alveoli → keeps oxygen concentration high and carbon dioxide concentration low → maintaining gradient.

Vertebrates and SOME invertebrates: O2 and CO2 concentration gradients are maintained by rapid blood flow through circulatory system.

Simple animals (flatworms, hydra, cnidarians, sponges): every cell in body close enough to external environment for gases to diffuse rapidly w environment.

Many multicellular organisms: bulk of body’s cells lack immediate access to environment → respiratory surface is thin, moist epithelium (respiratory organ).

Earthworms, SOME amphibians → skin serves as respiratory organ → beneath skin = dense network of blood capillaries facilitating gas exchange b/w environment and circulatory system. → skin is thin layer of epithelial tissue → shortens diffusion path → rapid diffusion.

Most animals = general body surface lacks sufficient area to exchange gases for whole organism → extensively folded/branched respiratory organs: gills, tracheae, lungs, to enlarge surface area.

In animals, the exchange of gases by diffusion between the internal and external environments of the organism is facilitated by the structure and function of the respiratory system.

Unicellular organisms exchange materials directly with external environment via simple diffusion across membrane.

Multicellular organisms: direct gas exchange between every cell and environment not possible, organisms have evolved adaptations to permit efficient gas exchange.

Invertebrates: Simple body plan → places many cells in direct contact with environment → direct exchange of materials.
Animals that lack simple body plan: highly folded internal surfaces, circulatory system.

Circulatory System: circulates tissue fluid (interstitial fluid) b/w tissue cells → shortens diffusion path → enables rapid exchange of materials via simple diffusion.

Interstitial (Tissue) Fluid: contains nutrients, respiratory gases, wastes.

In most animals: gas exchange facilitated by respiratory and circulatory systems.

Gills in Aquatic Animals:

Conditions for gas exchange vary depending on source of oxygen.

21% oxygen concentration in air, 1% in water.
Air less viscous and dense than water, allowing it to rush through narrow tubes and passageways → easier to breathe air → reduces need for efficient gas exchange.
Lower oxygen concentration, higher density, high viscosity of water = aquatic animals expend more energy to facilitate gas exchange.

Adaptations for efficient gas exchange

Gills: outfoldings of body surface, suspended in water.

Gill arch comprised of two rows of gill filaments.

Gill filaments composed of flattened plates (lamellae).

Lamallae lined with capillaries which pick up oxygen from water.

Countercurrent exchange: exchange of gases b/w blood and water flowing in opposite directions → blood has lower oxygen concentration than water it meets → large concentration gradient required for passive diffusion.

Aquatic Ventilation: Water flows past gills, oxygen diffuses into gills, carbon dioxide and water diffuse out.

Carried out by moving gills through water or moving water over gills.

Tracheal Systems (Insects)

Insects → hard exoskeleton → unsuitable for gas exchange.

Instead, respiratory gases exchanged b/w tissue cells and network of internal air tubes branching throughout body to increase surface area to volume ratio.

Trachea (largest tubes) connect to spiracles (external openings).
Air enters spiracle passes through trachea into smaller tubes - tracheoles

Tracheoles have moist epithelial lining and closed ends filled w/ fluid. Insect consuming large amounts of oxygen for respiration → fluid withdrawn into body → increasing surface area of tracheoles in contact with tissue cells.
Tracheae enlarge to form air sacs near organs requiring large oxygen supply.

Lungs: Respiratory organs in vertebrates and SOME invertebrates.

Fixed location inside body unlike tracheal systems which branch throughout body.

Respiratory surface of lung not in direct contact with other parts of body. Therefore, circulatory system transports gases between lungs and rest of body.

Amphibians = gas exchange across external body surfaces

Most reptiles, all birds and mammals = lungs for gas exchange.

Mammals → lungs located in thoracic cavity, enclosed by ribs and diaphragm.

Air enters nostrils and mouth
Flows through nasal cavity
Into trachea
Trachea branches into two bronchi (bronchus)
Bronchi repeatedly branch into thinner tubes (bronchioles) → Increase surface area for gas exchange.
Alveoli (Alveolus) at tips of bronchioles: tiny air sacs that facilitate gas exchange → Increase SA:V ratio

Oxygen in air dissolves into moist film lining epithelial tissue in alveoli → rapidly diffuses across epithelium into blood capillaries surrounding an alveolus. Carbon dioxide diffuses in the opposite direction.
Epithelial tissue lining alveolus and capillary = one cell thick → reduces diffusion path…
Constant blood flow through capillaries maintains oxygen and carbon dioxide concentration gradients required for passive diffusion.

Terrestrial Ventilation (Breathing)

Function: to maintain high oxygen and low carbon dioxide concentration at gas exchange surface.

Breathing: alternating inhalation and exhalation of air.

Muscles move ribcage upwards and outwards, expanding thoracic cavity
Diaphragm contracts and flattens, increasing lung volume, reducing air pressure in lungs
Air flows from higher pressure atmosphere to lower pressure lungs

🪻Describe the process of diffusion of respiratory gases as a passive process that does not require additional input of energy.

Diffusion of respiratory gases: passive process that does not require additional input of energy.