bio mod 2 yr 11

unicellular organism

organism composed of a single cell

colonial organism

collection of cells sharing resources and physically connected but with each cell performing all basic functions of life

multicellular organism

organism made of more than one cell in which different cells are specialised to perform different functions for the benefit of the whole

unicellular organism (structure)

• pro/eukaryotic

• single cell is responsible for all life processes

• always exposed to external environment

• microscopic size → high SA:V ratio

  • enables all required substances to move across cell membrane into all areas of cell + outside of the cell efficiently

colonial organisms (structure)

• colony: group of identical single-celled organisms

• some colonial organisms contain cells that have special functions

  • contributes to more efficient functioning of whole colony

volvox (colonial example)

• eukaryotic

• 500-60 000 algae cells

• each cell has 2 flagella and are connected by cytoplasm strands

• each cell contains chloroplasts → make own energy

choanoflagellates (colonial/unicellular example)

• eukaryotic

• each cell possesses an ovoid/round cell body with a single collared flagellum

• can exist both as unicellular or colonial

• may be evolutionary link between uni/multicellular organisms

multicellular organism (structure)

• made of specialised cells for different functions for the benefit of the whole organism

• specialised cells are incapable of living independently

• multicellular organisms are larger in overall size so total SA:V is smaller

  • passive transport of nutrients + wastes is inefficient

how multicellular organisms have efficient functioning

• cells maintain small size (high SA:V)

  • increases efficiency of diffusion of substances in/out of cell

• specialised cells

  • spreads workload across many different cells

• old/damaged cells are replaces (via mitosis)

  • organism continues to function (unicellulars can’t do this)

why cell specialisation is important for multicellular organisms

• if cells were not specialised each cell would have to perform every function (mrs gren) on its own

  • inefficient

• waste of nutrients + energy, much slower

cell specialisation

the particular function a cell has

cell differentiation

the process that a stem cell goes through to become specialised

stem cell

undifferentiated cell

where are stem cells located? (animals and plants)

• animals: embryo, human brain, bone marrow

• plants: meristematic tissue (e.g root and shoot tips)

cell hierarchy in multicellular organisms

organelle → cell → tissue → organ → organ system → organism

advantages of cell specialisation

• workload is spread amongst many cells

  • each cell has less/uses less energy

disadvantages of cell specialisation

• each cell can’t survive on its own

  • whereas in uni/colonial organisms they can

red blood cells (relate structure to function)

• function: transport oxygen around the body in the blood

• small size + bioconcave shape increase SA:V

  • allows rapid diffusion of oxygen

  • size allows it to fit easily into small capillaries

• absence of nucleus allows more haemoglobin to be carried in cell

palisade cells (relate structure to function)

• function: chloroplasts within the palisade perform photosynthesis

• found in upper layer of leaves → to efficiently capture sunlight falling on its surface

epithelial cells lining trachea / bronchi (relate structure to function)

• function: produce mucus, tiny hairs attached to cells brush foreign particles away

• composed on many tiny cilia → all beat synchronously

  • more efficient sweeping action

(animal) epithelial tissue

• covers body surfaces, protects organs, forms glands

• densely packed cells in sheets/layers

• no blood vessels, relies on underlying tissue for nutrients

• 2 types of surfaces: one exposed to outside and one exposed to adjacent tissue

• e.g alveoli in lungs

(animal) connective tissue

• has an extracellular matrix - composed of collagen and elastin

  • cells scattered throughout

• provides support and ensures different body parts are bound together + protected against damage

• e.g blood, tendons, ligaments

(animal) nervous tissue

• specialised for communication between parts of the body

• passes messages between themselves + other cells in body

• nerve cells have multi-branched dendrites to increase SA to receive messages + long axon extending from cell body to transmit messages

(animal) muscle tissue

• specialised for contraction

• all cells are elongated, contain actin + myosin (proteins), interacting to help them lengthen and shorten

justify hierarchical structure of organisation of cells

• without hierarchy, multicellular organisms would be very limited in size

• as a cell’s size increases, SA:V ratio decreases, meaning diffusion and osmosis would be insufficient in meeting the organism’s needs

• thus multi. organisms have evolved to have many specialised cells to spread the workload and to keep the organism functioning

(plant) meristematic tissue

• found at tips of roots + shoots, buds + rings around the stem

• cells are cube shapes + very small

• function: to produce new growth

(plant) dermal tissue

• function: protect it from damage + control interactions w/ surroundings

• makes up outer surface of plant

• most cells lack chloroplasts

• cells may secrete waxy layer (cuticle)

  • vital to minimise plant’s water loss

• some cells have root hairs, increase SA for diffusion of water into roots

(plant) vascular tissue

• function: transport of substances around the plant

• found in roots, stems and leaves

xylem function

transports water and mineral ions

phloem

conductive tissue composed of thin-walled cells;

transports dissolved sucrose and other photosynthesis products around the plant

(plant) ground tissue

• all of the internal cells of a plant other than vascular tissue

• responsible for food storage, support, etc.

root system (relate structure and function)

• function: anchoring plant, absorbing water + inorganic nutrients from soil, cellular respiration

• no chloroplasts → not exposed to sunlight

• large SA allows water + minerals to be absorbed efficiently

  • extensive branching of root systems

  • root hairs increase SA up to 12x

how do substances move into the roots?

• water → via osmosis

• mineral ions → by faciliated/diffusion or active transport

• oxygen diffuses into root cells, CO2 diffuses out

shoot system: stem (structure + function)

• stem provides structural support + transport path between roots + leaves

• 3 main tissues in stem

  • dermal (outer layer)

  • vascular (xylem + phloem)

  • ground (everything else)

shoot system: leaves - relate structure to function (absorbing sunlight)

• thin flat, structure - increases SA

  • maximum absorption of light by chlorophyll

• epidermis is transparent → allows sun to penetrate to photosynthetic cells below

• palisade cells - contain many cells lined up near upper surface to absorb sunlight

shoot system: leaves - relate structure to function (gaseous exchange)

in epidermis, guard cells control gas exchange and loss of water through leaf

xylem consists of:

vessels: long thin, continuous tubes made of dead tissue with lignin-strengthened walls

tracheids: long structures w/ end walls that overlap

transpiration-cohesion-tension theory (TCT)

• concentration of water vapour outside the leaf is lower than inside leaf (OR humidity OR light OR darkness) → diffusion of water out of the leaf (FROM STOMATA) (transpiration)

• water molecules evaporating from leaf surface pull adjacent water molecules w/ them (due to cohesive properties of water)

• water in xylem vessels below is then drawn up to the leaves to replace water lost through evaporation (due to adhesive properties of water)

• in this process, leaf cells all drawing water from the xylem create tension that pulls water up xylem vessels from the roots

factors aiding water movement up roots (in TCT theory)

• cohesion: force of attraction between like molecules

• adhesion: force of attraction between unlike molecules

• cohesion between water molecules and adhesion between water molecules and xylem walls maintain water column

• small amount of root pressure forces water already present in xylem push water upwards

tension

continuous negative pressure caused by the drawing up of water through stem towards leaves

phloem consists of:

• sieve tube cells - long, thin phloem cells that have sieve plates through cell walls

• companion cells

  • provide ATP + nutrients

  • assist loading and unloading of sugars into sieve tube cells

translocation:
mechanism of flow is provided by…

an osmotic pressure gradient, generated by differences in sugar and H2O concentrations

translocation: step 1

plants obtain sugars through photosynthesis

translocation: step 2

active transport is used to move sugars from sugar sources into phloem, against concentration gradient

translocation: step 3

increased concentration of sugars in phloem causes water to move passively into phloem from xylem by osmosis

translocation: step 4

the increased fluid volume in phloem creates a temporary pressure increase, causing movement of materials in the phloem towards sinks

translocation: step 5

sugars move into sinks, via active or passive transport

translocation: step 6

the decreased concentration of sugars in the phloem causes water to move passively back into xylem, reducing pressure in the phloem

magnetic resonance imaging (MRI)

• uses radio waves + magnetic field to take series of images

  • combined on a computer to form 3D image

• application: grow plants in clear containers - structure of roots can be analysed in detail on a computer

x-ray computed microtomography (micro-CT)

• non destructive process

• sample positioned in an x-ray beam is rotated + hundreds of images from different angles are taken

  • constructed into a 3D image on computer

• application:

  • gain deeper knowledge of plant’s internal structure

  • any angle can be observed - spatial arrangement of tissues can be studied

van helmont (1580-1644) (what did he theorise, experiment?, what did he conclude)

• thought soil formed all plant matter

• after 5 years of growing his plant (no added soil), plant has a large increase in mass

  • concluded all plant matter came from the water he added

• his conclusion was incorrect

  • didn’t consider gases in air

  • no repetition - unreliable

  • didn’t measure how much water he added - inaccurate

joseph priestly (1733-1804) (what did he theorise, experiment?, what did he conclude)

• noticed in an enclosed space if a candle goes out and a mouse dies

• he put a mint plant in the jar, and the candle stayed lit + mouse stayed alive

  • concluded plant “restores” air to whatever the candle + mouse removed

• greatly contributed to understanding of photosynthesis

radioisotopes

forms of an element that emit radiation

how is the pathway of glucose produced in ph/syn traced using radioisotopes?

• carbon-14 is added to carbon dioxide supply of plant

• carbon-14 then takes part in photosynthesis reactions and is incorporated into glucose molecules produced

• glucose molecule’s pathway can be traced using the radiation emitted by carbon-14 and recorded in an autoradiograph

how is oxygen traced in plants using radioisotopes?

• Radioisotopes used to find out whether oxygen released during PS came from the oxygen atom in water or from the oxygen atoms in CO2

• Plants were given water containing radioactive oxygen

• showed all radioactive oxygen released as oxygen gas

  • showed water (NOT CO2) was oxygen gas released in ph/syn

characteristics of gas exchange structures in animals (to ensure efficient functioning + max. gas exchange)

• large SA - allows more efficient rate of diffusion to supply oxygen and remove CO2

• close proximity to efficient transport system to transport gases to and from cells in organism - e.g alveoli located next to capillaries

• greater concentration of required gas on one side of membrane so concentration gradient is maintained

• moist, thin surface

  • ensures gases dissolve for easier diffusion

  • thinness decreases distance gases need to travel

characteristics of alveoli as gas exchange surfaces

• increased SA - 300 million microscopic alveoli supplied by 280 million capillaries

• alveolus wall - flattened cells, 1 cell thick

• oxygen diffuses from alveoli (more concentrated) into capillaries (less concentrated)

• its moist - enhances efficiency of diffusion

respiratory systems in fish

• concentration of gases is much lower than in water - they have low solubility in water

• water flows in one direction - entering the fish’s open mouth as it swims

• water flows over front of the gills + leaves fish through gills slits

  • gaseous exchange takes place at the gill-water interface

• countercurrent flow of blood and water keeps concentration gradient of oxygen outside fish (in the water) higher than in the blood for max. diffusion of oxygen to the blood

respiratory systems in insects

• have tracheae - network of tubing

  • take in + expel air through spiracles

  • tubes connect to all insect’s tissues - supplies oxygen directly to cells for respiration

  • have valves to regulate opening/closing of spiracles - so they don’t dry out

• not very efficient - limits size of insects

• when insect is active - more spiracles open to increase respiration