Cells and Living processes


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  • Created on: 24-03-11 20:39

Cells and Living Processes

Characteristics of living things -

Living organisms share 7 characteristics: movement, respiration,sensitivity, nutrition, excretion, reproduction and growth.

Living cells contain special structure so each carry out a particular function.

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Organelles and Ultrastructure

- see a large nucleas under a microscope. Detail inside of cells revealed by electron microscope - cell's ultra structure.

-Division of labour

Most organelles found in both plant and animal cells. Same function with each cell. Each type of organelle has a specific role within the cell. This is called division labour. Different organalles work together in a cell contributing it's part to survival in the cell.

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Movement and stability in cells


Cells contain a network of fibres made of protein - keep the cell's shape stable providing internal framework called CYTOSKELATON.

Some fibres called actin filaments are like fibres found in muscle cells - able to move against eachother - fibres cause movement inside white blood cells.

Other fibres known as microtubules. They are cylinders 25nm diameter. Made of protein called tubulien.. Microtubules may be able to use to move a microorganism through a liquid or waft a liquid past the cell.

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Undulipodia - cilia exactly the same structure.

- Hair like extensions that stick out from the surface cells. Each one made up of a cylinder contains 9 microtubules. 2 microtubules in the central bundle.

Undulipodia are longer than cilia.

- Undulipodia that forms the tail of a sperm cell can move around the whole cell.

In the ciliated epithelilal tissue, the sweeping movement of the cilia moves subtances as the mucus across the surface cell.

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Undulipodia and cilia can move because the microtubules can use energy from ATP.

First seen under light microscope.

Cilia are short ( occurs in large numbers of cells) - undulipodia are long  ( ones or twos in a cell )

- some bacteria have flagella, internal structure is very different.

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Vesicles and Vacuoles

- vesicles are membrane bound sacs found in cells. Used to carry many different subtances around the cell.

- plant cell the vacuole maintains cell stability. Filled with water and solutes so it pushes cytoplasm against cell wall - making cell turgid. Helps to support plants. Important to non woody plants.

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Plant cell walls

- these are outside the plant cell plasma membrane. ( cell surface membranes )

- plant cell walls made of cellulose - a carbohydrate polymer made of glucose subunits.

- cellulose forms sieve like network of strands to make the wall strong.

- held by a rigid pressure of fluid inside the cell - supports cells and the whole plant.

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Nucleas - largest organelle. When stained shows darkened patches know as chromotin. Surronded by nuclear envelope. Structure made of 2 membranes fluid between them Holes and nuclear pores go through the envelope. large enough for large molecules to pass through. Dense sphereical structure called nucleoulous inside the nucleas.

Fuction - houses all the genetic information material.

Chromotin consists DNA and proteins. Protein regulates cells activities.

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Endoplasmic Reticulum (ER)

ER consists of flattened membranes bound sacs - cisternae. Continuous with outer nuclear membrane.

rough ER - studded with ribosomesm. Smooth ER does not have ribosomes.

- Rough ER transports proteins that were made or attatched ribosomes. Proteins may be secreted from the cell.

Smooth ER involved in making lipids that the cell needs.

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Golgi appartus

A stack of membrane bound flattened sacs.

- recieves proteins from the ER and modifies them - may add sugar to the molecule.

the golgi appartus then packages the modified proteins into vesicles.

Some modified proteins may go to the surface of the cell so it can be secreted.

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Spherical sausage shaped - two membranes seperated by a fluid filled space. Inner membrane is highly folded form cristae - central part of mitochondrion called matrix.

Function - Site where ATP is produced during respiration. Universal carrier of all activities that need energy in the cell - driven by energy release ATP.

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- found only in plant cells. Have 2 membranes with fluid filled space.

- site of where photosynethesis takes place. Light energy used to drive reactions of photosynthesis which carbohydrate molecule are made from carbon dioxide and water.

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Spherical sacs surronded by a single membrane.

- Lysosomes contain powerful digestive enzymes. Role to break down materials.

Organelles WITHOUT membranes surronding them.

- Ribosome : Tiny organelles contains 2 subunits - site of protein synthesis in cell (new proteins are made). Coded information mRNA nucleas is used to assemble proteins from amino acids.

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- small tubes of protein fibres (mictotubules ) pair of them next to the nucleas in animal cells and cells of protocistists.

- take part in cell division, form fibres known as spindles which move chromosones during nuclear division.

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Organelles at work

Division of labour - hormones are chemical messenger molecules coordinate activities of the whole organisms.

- instruction to make hormones are in the DNA in the nucleas.

- specific information to make the hormone known as a gene - chromosone.

- the nucleus copies the instruction in the DNA into a molecule called mRNA.

- mRNA molecule leaves the nucleas through nuclear pore and attatches to a ribosome.

- ribosomes reads instructions and used the code to assemble the hormone (protein)

- the assembled protein in the rough ER pinched off in a vesicle and transported to the golgi appartus.

- the golgi then packages the protein and modify so it's ready for release. Packaged and moved to the cell surface where it is secreted outside.

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Prokaryotes and eukaryotes

Eukaryotic cells have a nucleas -

organelles - give cells a complicated internal structure - performs a specific role. Eukaryotic cells means having a TRUE nucleas. All organisms apart from prokayotes have this cell structure.

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Prokaryotes do not have a nucleas

They are bacteria - 1 -5 much smaller than eukayotic cells. But show all characteristics of living organisms.

- only have one membrane cell surface membrane around the outside.

- surronded by cell wall - usually made of peptidoglycan NOT cellulose.

- contain ribosomes that are smaller than eukaryotic ribsomes.

- DNA in cytoplasm form single loop 'bacterial chromoson' unlike seperate strands of eukaryotes. Many contain very small loops of DNA called plasmids.

-DNA not surronded by a membrane - DNA lies in a nucleoid.

- ATP production takes place in specialised infolded regions cell surface membranes call mesosomes.

- prokaryotic cells have flagella.

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Prokaryotes and disease

- some prokarytoic or bacterial cells are well known because of the disease they cause,

- some stains of bacteria are resistance to antibiotics MRSA.

Prokaryotics that help - important to humans -

- food industry uses particular bacterial species eg cheese and yogurt.

- mammalian intestines, bacterial cells help with vitimain K production help digest some foods.

- skin is covered with a normal flora of bacteria - prevent harmful organisms getting into the body.

- sewage treatment and natural recycling rely on bacterial cells digesting and respiring dead and waste material.

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Biological membranes - fluid boundries

Membranes - sepearting the cells contents from the outside world.

- Roles of membranes:

- seperating cell contents from the outside enviroment.

- seperating cell components from cytoplasm

- cell recognition and signalling

- holding componenets of some metabolic path ways in place.

- regulating transport materials into or out of the cells.

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Nature of phospholipids

Phospholipid bilayer - structural component of plasma membranes - 2 layers of phospholipid molecules. Proteins embedded in this layer.

- Phosphate 'head'  hydrophilic - water attracting. Phosphate 'tail' two fatty acids hydrophobic - water repelling. Do not easily dissolve or mix in water. Repel water molecules. Molecules with unevenly distrubuted charges can interact with water molecules easily.

Phosphate head sticks into water while to the two fatty acids stick out of the water.

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Layers and bilayers

If phospholipid molecule is completely surronded by water - bilayer can form.  Hydrophobic tails are held away from water molecules. Phospholipid molecules can move freely. Hydrophilic head group cannot pass through hydrophobic region in the middle of bilayer. Gives bilayer stability despite the molecules not being bonded together.

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All membranes are basically the same

- hydrophobic layer formed by phospholipid tail creates barrier to many molecules and seperates the cell contents from the outside world. - Metabolic reactions take place in a water based enviroment.

Permeability - All membranes permeable in water molecules because water molecules can diffuse through lipid bilayer.

- cell membranes that are permeable to water and some solutes are describes as partially permeable membranes.

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Fluid mosaic model

- fluid mosaic describes the molecular arrangements on membranes. Main feature are -

- bilayer of phospholipid molecules forming basic structure.

- various protein molecules floating in phospholipid bilayer - completely freely - some bound to other components or to structures within the cell.

- some (extrisic) proteins partially embedded in the bilayer on the inside our outside face , other (intrinsic) proteins completely spanning the bilayer.

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Glycoproteins and glycolipids

- Some of the phospholipid molecules making up the bilayer and some proteins found in the membranes - small carbohydrates attatched to them,

- where phospholipid molecule have carbohydrate part attatched they are call glycolipids.

- where protein molecules have carbohydrates attatches they are called glycoproteins.

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Membraine componenets and their roles

- membrane stability and fluidity.

- chloresterol - gives membranes of some eukaryotic cells mechanical stability. Steriod molecule fits between fatty acid tails and helps makes barrier more completely so substances like water molecules and ions cannot pass easily and directly through the membrane.

Membraine transport functions.

- channel proteins: allow movement of some subtances across the membrane. Molecule of sugars such as glucose are too large and hydrophilic to pass directly through the phospholipid bilayer, instead they enter and leave through PROTEIN CHANNELS.

- carrier proteins: actively move some subtances across membrane. When minerol ions actively transported into root hair cells, lower the water potentional of those cells. Makes water enter by osmosis - nitrate ions are actively transported into xylem vessels to lower the water potentional cause water to take from the surronding root cells.

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Recognition and communication

- receptor sites: some allow hormones to bind with cells so that a cell ' response' can be carried out. A cell can only respond to a hormone only if it has a receptor for that hormone on it's cells surface membrane. Cell membrane receptors are important so allowing druges to bind and so affect cell metabolism.

- Glycoproteins and glycolipids may be involved in cell signalling that they are 'self' to allow recognition by the immune system. Glycoproteins can also bind cells together in tissues.

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Metabolic Processes

- enzymes and coenzymes. Some reactions in photsynthesis take place in membranes inside chloroplasts - some stages of repiration takes place in membranes of mitochondria.

- Enzymes and coenzymes may be bound to these membranes - the more membrane there is the more enzymes and coenzymes it can hold.

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Membranes and temperature

Increasing temp gives molecules more kientic energy so they move faster. Increased movement of phospholipid and other components makes membranes leaky which allow subratnces that would not normally do so enter and leave the cell.

eg. beetroot  - sections of beetroot tissue exposed to increasing tempereatures release more and more of the red pigment found in the cells as the cell surface membrane and vacuole membrane are damaged by heat.

- organisms that live in a very hot or cold enviroment need differently adapted molecular components of their membranes for eg chlorestrol content so their membranes can perform the function they need in life.

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Crossing membranes 2 - active processes

- concentration gradient don't always help - cells cannot always be met by diffusion. Cells may need to move materials into or out of the cell more quickly than simple diffusion allows.

-magnesuim ions often short supply in soil. Plant cells need them to make chlorophyll. Plant cell must be able to move them in and out of cell more quickly than simple diffusion allows.

- active transport helps absorbs gluscos from intenstines.

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Active transport

Active transport - movement of molecules or ions across membranes uses ATP to drive protein within membranes.

- some carrier proteins found in membranes act as pumps. - similar to protein carriers used for faciliated diffusuion - shaped in a way that fits (complementry) to the molecule they carry. Carry larger or charged molecules and ions through membranes. These are molecules and ions that vannot pass through lipid bilayer by diffusion.

  • carry specific molecules one way across the membrane
  • in carry molecules across the membrane - use metabolic energy in form of ATP.
  • carry molecules in the opposite directions to concentration gradient.
  • carry molecules in faster rate than diffusion.
  • molecules can be accumlated either inside cells or organelles out outside.
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Ensuring one way flow

  • - energy used in pumping molecules across membranes by active transport changes the shape of carrier protein.
  • shape change means that specific molecule needs to be transported - or pumped fits into carrier protein on one side of membrane only.
  • as molecule being carried through - carrier uses energy ATP. Changes its shape - so molecule being carried across now leaves carrier protein.
  • the molecule cannot enter the transport protein - protein now has a different shape so it will not fit.
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Calcium ion movement- in muscle

  • muscle fibres can only contract only if calcium ions are present.
  • when muscle is stimulated to contract calcium ions are released from membrane bound stores - they are in high concentration.
  • when muscle needs to relax again - calcium ions are pumped rapidly back into stores by many calcium ions pumped on the membrane of specialised endoplasmic reticulum
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Moving in large amounts - bulk transport

  • some cells need to move in large quantaties of material in or out.
  • Process is endocytotis - involves bringing materials into the cell.
  • Exocytotis involves material coming out of the cell.
  • Bulk transport is possible because membranes can easily fuse - seperated and 'pinch off'.
  • bulk transport requires energy ATP  - the energy is used to move the membranes around to form vesicles that are needed to move the vesicles around the cell.
  • examples - Hormones: pancreatic cells make insulin in large quantaties - insulin processed and packaged into vesicles in golgi app - these vesicles fuse with outer membrane to release insulin in blood.
  • plant cell
  • white blood cells.
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Water - special case

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Water is a special case

- water molecules free to move diffuse from a high region to a low region.

- any substance dissolved in water - will affect concentration of 'free' water molecule. Substance that dissolve called soule - a liquid dissolved called - solvent combine two together called solution.

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Water potentional - concentration of 'free' water

  • water potentional measure of the tendency of water molecules to diffuse one place to another.
  • - water always moves from a region of high water potentional to a region of lower water potentional. high concentration of free water molecules to low concentration of water molecules.

eg. first bucket contains pure water - all water molecules free to diffuse - pire water highest concentration of freely moving water molecules - highest water potentional.

As solute dissolves water molecules cluster around them forming solution - lowers the concentration of free water molecules - lowers water potentional - the more solute is dissloved the lower it is in the solution.

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Special kind of diffusion - refers to only to the movement of water molecules.

- by diffusion

- across a partially permeable membrane.

osmosis movement of water molecules from region high water potentional to low water potentional down a water potentional gradient across partially permeable membrane.

- as with diffusion - net movement of molecules occurs until the concentration are evened out - so osmosis will occur until water potentional is the same on each side of the membrane.

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Osmosis, water potentional and cells

- water potentional in cells is lower than that of pure water, because of sugars, salts and other substance dissolved in cytoplasm.

- in plant cells vacuole also contains dissolve subtsnaces.

- water potentonal measured in kilpPascals - pure water has highest water potentional of -kPa - disscolving solute in water reduces the water potentional.

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New cells - parent and daughter cells

- cell cycle describes the events that take place as one parent cell divides to produce two new daughter cells which then grow to full size.

- for some organisms - cell cycle is the life cycle - each daughter is a new single celled organism. daughter cells must carry out the same function as a parent cell.

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Chromosones have instructions

- chromosones are in the nucleas of eukaryotic cells.

- each chromosone contains one molecule of DNA which includes specific genes.

- chromosones hold instructions, called blue print for making new cells. Daughter cells produced during the cycle must contain a copy of all these instructions - contain full set of chromosones copied exactly from the chromosone of the parent cell.

- humans there are 46 chromosones - in onion cells 12 - chimpanzee haves 48 and dogs have 78.

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Copying and Seperating

in eukaroyotes, the molecules of DNA make up each chromoson are wrapped around proteins called histones. DNA _ histones protein = chromatin.

- before a cell can divide to produce two new daughter cells - the DNA of each chromosone must be replicated.

- two replicas are produced - each an exact copy of original - remain held together at a point called centromere - plays an important role in nuclear division.

-each chromosone consists of 2 replica DNA strands- called pair of sister chromotids - when they are sperated from eachother each one will end up in a different new daughter cell.

before this happens the chromotin must be coiled up (superciol) to form visible chromosones - each one is then engouh to move around easily. chromosones can take up stains and seen under a light microscope.

- super coiled chromosones cant perform their normal functions in cell - so length of time they spend coiled up needs to be short as possible.

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Checks and Balance

- as chromosones are being replicated - proof reading enzymes move along the new DNA strand and check the copying has been done properly.

- if genes are not copied properly the resulting mutations may mean the new cell may fail to function.

- copying the information carried by the DNA in human each time the cell divides is roughly equivelent to copying out of a full 30 volume set of encyclopedia britaannia 20 times over without making mistakes.

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How fast is the cycle?

- the length time taken of parent cell to divide to 2 new daughter cell and to grow full size depends varies between species and cell type, also affected by avability of nutreints for cells

  • Cell cycle
  • interphase - DNA replicates in this stage
  • mitotis - the nucleas divides and chromotids seperate.
  • cytokinesis - cytoplasm divides or cleaves
  • growth phase - each new cell grows to full size.

Mitosis occupies a small proportion of cell cycle and remaining larger portion include copying and checking genetic information of DNA and processes associated with growth.

Daughter cells need membranes cytoplasm all of its new parents cell to carry out metabolic functions.

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Two nuceli from one

- produce genetically indentical daughter cells

- asexual reproduction - single celled organisms divide to produce 2 daughter cells that are seperate organisms - some multi cellular offspring from a parent.

- Growth - multicellular organisms grow by prodcing extra cells - each new cell genetically identical to parent cell so it can perfom the same function.

- repair - damaged cells need to be replaced by new ones so it can perform the functions so it needs to be genetically identical.

- replacement - red blood cells and skin cells are replaced by new ones.

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Mitotsis in 4 stages

Nuclear division where 2 genetically identical nuclei are formed from one parent cell nucleus - prophase, methaphase, anaphase and telophase.

  • prophase- replicated chromosones supercoil (shorte and thicken)
  • metaphase- replicated chromosones line up down the middle of the coil
  • anaphase - the replicas of each chromosome are pulled apart from eachother.
  • telophase - two new nuclie are formed.
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Chromosomes become visible in prophase

  • each chromosone already replicated in interphase.
  • Prophase chromosones shorted and thickened and using a light microscop - they consist a pair of sister chromotids
  • Nuclear envelope breaks down and disappears - organelle called centriole divides into 2 each daughter centriole moves to opposite ends to form spindles.

- Chromosones line up in metaphase

chromosomes move to the central region of the spindle (equator) each becomes attatched to a spindle thread by its centromere.

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Replicated chromosones seperated in anaphase

The replicated sister chromotids are seperated from eachother - each sister becomes individually chromosone. Each identical - original from parent cell from which its copied.

- spindle fibres shorten- pulling sister chromotids futher and further away from eachother towards the poles.

  • Two nuclei from in telophase
  • As seperated sister chromotids reach poles of each cell - a nuclear envelope forms around each set.
  • Spindle breaks down and disappears - chromosone uncoils - you can no longer see it under a microscope.
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Two new cells can now be made

- the whole cell now splits to form two new cells , each one containing a full set of chromosone identical to that - found in original parent cell. Splitting in two is called cytoskenis.

- having identical genetic information - form identical chromosones means daughter cell is capable of doing everything a parent cell can do.

- a time and place

  • animals capable of mitosis and cytokinesis - plant special cells meristem cells can divide in this way.
  • plant cells do not have centrioles - tubeliun protein threads are made in cytoplasm.
  • animal calls cytoskinesis happens from outside - plant in happens inside near equator. New cell membrane and new cell wall material is laid down along the cell plate.
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Cell Specialisation

Size matters- Eukaryotic cells have different organelles performing to a particular function. All contribute to the survival of the cell.

From the mitochondria releasing energy for the cell's need to the ribosomes assembling cell proteins, each organelle contributes to process needed to sustain life.

- physical limit to the size that a single cell can reach. - goverened by the need to support structures within cell and by increasing diffuculty of getting enough oxygen and nutrients into a cell to support its needs as its size starts to increase.

Single celled organisms have large surface area to volume ratio - they can recieve oxygen and remove carbon dioxide by diffusion through membrane.

- multicellular organism have smaller surface area to volume ration and not all cells are in contact with the external medium - meaning they need specialised cells - forming tissues and organs to carry out particular functions - include delivery of oxygen and nutrients and removal of waste.

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Differentation and specialisation

when organisms consist of many cells - some cells will be different from others - some cells perform one role very well. Specialised in that role while other cells are specialsed for other roles.

- Differentation - refers to the changes occuring in cells of a multicellular organisms so that each different type of cells becomes specialsed to perform a specific funtion.

cells can differentiate in a number of ways

  • the number of a particular organelle
  • the shape of the cell
  • some of the contents of the cell - involve three types of change.
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Erthrocytes and neutrophiles

Erythrocytes (red blood cells) and neutophils ( white blood cell ) play different roles

- both are human cells both began with the same set of chromosones - potentionally capable of carrying out the same functions.

- all blood cells produced from undifferentated stem cells in bone marrow.

- the cells destined to become erthrocytes lose their nucleus, motichondria, golgi appartus and rough endoplasmic reticulum - packed full of the protein haemoglobin. Shape of cells changes so they biconcave discs - capable of transporting oxygen from lings to tissues.

cells destined to become neutrophils keep their nucleas - cytoplasm appears granular because enormous numbers of lysosomes are produced.

- role of neutrophils in blood is to ingest invading microoganisms - so all those potent enzymes in the lysosomes enable the neutrophiles to be specialised for killing microorganisms.

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Organising the organism tissure, organs and system

- organisms consisting of millions of cells - activites and funtions of all cell types need to be organismed to ensure that the whole organism can survive.


  • a collection of cells similar to eachother perfom similar funtion.
  • Maybe found attatched to each other - eg xylem phloem nervous tisues


  • collection of tissues working together to perform particular function called an organs - eg leaves liver in animals

Organs systems

  • made up of a no. of organs working together to perfom overall life function.
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Organising the organism

Transport in tissues - xylem and phloem

- plants need to move water and minerals from the soil through their roots and stems and up into the leaves - move products of photosynthesis from the leaves to other parts of the plant to use for growth or to store for later use. Xylem and phloem come from dividing meristem cells such as cambium - undergo differentation to form other kind of cells in the transport tissues.

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Xylem tissue consists of xylem vessels with parenchyma cells and fibres - meristem cells produce a small cells that elongate - their walls become reinforced and waterproofed by deposits of lignin - kills the cells content - ends of the cells break down so that they become continious long tubes with wide lumen.
Xylem tissue is well suited for transporting water and minerals up the plat - it also helps to support the plant.

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Phloem tissue

Phloem tissue consist of sieve tubes and companian cells - the meristem tissue produces cells that elongate and line up end to end to form a long tube - ends do not break down completely form sieve plates between cells - sieve plates allow movement of materials up and down the tubes - next to each sieve tube is a companian cell - they are metabollicaly active their activies play an important role in moving the products of photosynthesis up and down the plant in the sieve tubes.

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Forming a lining - epithelial tissue in animals

Animal tissues groups into four main catergories

  • epithelial tissue - layers and linings
  • connective tissues - holds structures together - provide support ( cartilidge bone blood)
  • muscle tissue - cell speciailised to contract and move parts of the body.
  • Nervous tissue - cells that can convert stimuli to electrical impulses and conduct those impulses
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Squamous epithelila tissue

  • - made of cells that are flattened, very thin.
  • cell together form a thin smooth flat surface - makes them ideal for lining insides of tubes such as blood vessels - where fluids can pass easily over them
  • Squamous epithelil tissue also forms thin walls such as walls of the alveoli in the lings - provide short diffusion pathway for the exchange of oxygen and carbon dioxide.

the squamous cells are held in place by the basment membrane - secreted by epithelial cells - made of collagen and glycoproteins - basment membrane attatches epithelial cells to connective tissues.

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Ciliated epithelial tissue

  • made up of colum shaped cells - this type of tissue often found on inner surface of tubes - eg. in the trachea, bronchi and bronchioles ( airways in lungs) and in the utera and oviducts - part of the cell surface that is exposed in the tube speace ( lumen)  - covered with tiny projections called cilia - some cells produce mucus - cilia wave in a synchronised rhythm and move the mucus
  • in the breathing tract - small particales and micro organisms are trapped in the mucus.
  • the cilia waft it back of the throat to be swallowed
  • Problems - smoking that nicotine in the smoke paraylses the cilia - so they cant sweep to move the mucus. Cilia also become damaged by the tar in the smoke and are destroyed fewer of them.
  • Mucus becomes trapped in the lungs and the microbes can't be cleared out of the airways to be killed by the stomach acid.

-rhythmetic waves generated by ciliated epithelium move egg cells from the ovary along the oviduct.

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Harvesting Light - cooperation in action

- leaves are major organs of photsynthesis in a plant.

  • their cells tissues and overall shape are arranged to help MAXIMISE the rate of PHOTSYNTHESIS. Requirements
  • light
  • a supply of water
  • a supply of carbon dioxide
  • the presence of chlorophyll.

As the products of photsynthesis build up they need to be removed - where they're needed - waste product oxyfen gas must be excreted.

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Harvesting light

- in order to balance these - the leaf is adapted ina no. of ways

  • transparent upper surface layer - upper endermis lets light through.
  • a palisade layer underneath consists of long thin tightly packed cells containing a lot of chloroplast that contain chlorophyll.
  • a loosely packed spongy mesophyll layer has many air spaces to allow circulation of gases.
  • low epidermis layer has pores called stomato - allow gases to be exchanged between leaf and outside air - the stomata each have two guard cells that can swell to open the pore - when guard cells are not turgid - stoma closes.
  • A leaf vein system contain xylen and phloem tissue supports the leaf as well as carrying the transport tissues - these tissues transport water into the leaf and products of photosynthesis out of the leaf to other parts of the plant.
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Opening and closing stomata - role of guard cells

- guard cells are specialised cells that appear in pairs on the lower epidermis - unlike lower erpidermis - they contain chloroplast and cell walls contrain spiral thickiening of cellulose.

- when water is move into these cells they become turgid and because of the sporals in the walls of the innder edges - only outer walls stratch - two guard cells bulge at both ends so a pore opens between theme - pore known as STOMATA.

Locomotion - sysytem cooperation

as muscles and nerves work they use energy - require a supply of nutrients and oxygen from circularoty system and tun reviseve these chemicals from digestive and ventilation systems.

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