OCR AS Biology Unit 1: Cells, Exchange and Transport

OCR AS Biology Unit 1: Cells, Exchange and Transport

To understand and discuss the basis of cell theory based upon milestones in cell biology

To carry out practical work on cell size and magnifications using a light microscope

To be able to draw a plant cell and an animal cell using a light microscope

To prepare slides using stains to identify cell structure.

Read through handout

Group discussion Discuss the impact of the microscope on

cell biology List things you think are the most

important

The cell is the fundamental unit of life. All organisms, whatever their type or size, are composed of cells. The modern theory of cellular organisation states:- All living things are composed of cells and cell

products. New cells are formed only by the division of pre-

existing cells The cell contains inherited information (genes), which

is used as instructions for growth, functioning and development.

The cell is the functioning unit of life; the metabolic reactions of life take place within the cells.

Before the development of cell theory, it was commonly believe that living organisms could arise by spontaneous generation.

Explain what this term means and why it has been discredited as a theory.

When Scientists began to observe cells, they started with simple microscopes

There are two different types of microscope both use a form of radiation to create an image of the specimen: Light microscope – uses light Electron microscope – uses electrons

Magnification Number of times larger an image is

compared with the real size of the object

Resolution The ability to distinguish between two

separate points

For the microscope in front of you, work out The magnification of each lens The field of view for each lens ▪ Using a graticule / stage micrometer

Collect a prepared slide of Squamous epithelium, draw what you can see. Your diagram should include title, labels,

magnification and a scale bar.

Strip a pieces of epidermis from the inner lining of one of the fleshy scales of an onion.

Mount it in dilute iodine solution▪ Observe and draw a cell under low power and high

power

Repeat the above procedure using water instead of iodine.▪ what difference does this make to how much you can

see?

What does this tell you about the value of staining cells before you look at them under the microscope?

Make sure all diagrams have a title, label, magnification and scale bar.

OCR AS Biology

Light microscope▪ Long wavelength▪ Can only distinguish between two objects if

they are 0.2µm apart.Electron microscope

▪ Shorter wavelengths▪ Can distinguish between objects 0.1nm apart

ionmagnificat

imageofsizeobjectofsize

How many times bigger the image is compared to original subject.

If asked to calculate the size of an object

objectofsize

imageofsizeionmagnificat

When calculating magnification make sure the units of length are the same for both object and image

unit symbol Equiv. in m

Kilometre km 103

Metre m 1

Millimetre mm 10-3

micrometre µm 10-6

nanometre nm 10-9

Object 100nm in lengthHow much is it magnified in a photo?Measure object in photo (10mm

long)

nm

mm

objectofsize

imageofsize

100

10

The measurements need converting to the same unit (usually the smallest)

There are 10 000 000nm in 10mmMagnification is:

100 000 times

OCR AS Biology

Two main advantages High resolving power (short wavelength

of electrons) As electrons negatively are charged the

beam can be focused using electromagnets

As electrons are absorbed by molecules of air, a near-vacuum has to be created within the chamber of an electron microscope.

Two types Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM)

Activity Read through the handout on the

electron microscope Answer discussion questions 1 - 4

Light MicroscopeAdvantages

Electron Microscope Disadvantages

Small and portable very largeOperated in special rooms

Unaffected by magnetic fields Affected by magnetic fields

Preparation of material is quick and simple

Preparation of material is lengthyRequires expertise

Material rarely distorted by preparation

Preparation may distort material

Natural colour of object observed

Images are in black and white

Cheap to purchase and operate

Expensive to purchase and operate

Light MicroscopeDisadvantages

Electron MicroscopeAdvantages

Magnifies objects up to 1500x only

Magnifies objects more than 500 000X

Depth of field is restricted

Possible to investigate a greater field of depth

Comparison of pathways of the light and electron microscopes

Ultrastructure of an animal cell as seen through an electron microscope

Cell structure Read through the information on each of

the organelles as you colour them in Follow the guidance on colouring them

in given at the bottom of the page

This works on the theory that whilst you are colouring in, you have time to consider and think about the structure and function of the organelles

OCR AS BiologyFOUNDATION

In pairs label the diagram of the animal cell given. How many structures can you identify? Look at the cells alive animation – how

many have you correctly identified?

Label the paper copy of the diagram of an animal cell

In pairs label the diagram of the plant cell given. How many structures can you identify? Look at the cells alive animation – how

many have you correctly identified?

Label the paper copy of a diagram of a plant cell

Using the cards, match up organelle, position and function.

Organelle Position Function

Nucleus Within cytoplasm Contains genetic code which controls the activities of the cell

Cytoplasm Around nucleus Location of chemical reactions – does the work of the cell

Cell surface membrane

Around cytoplasm Controls exchange of substances between cytoplasm and surroundings

Cell wall around cell membrane

Gives cells rigidity, stops it bursting if put in water

Cell vacuole Within cytoplasm Affects concentration of cytoplasm. Is a store of inorganic ions.

Tonoplast Around cell vacuole Controls exchange of substances in plant cells between vacuole and cytoplasm

Large granules Within cytoplasm Usually stores food e.g. starch


Nuclear envelopeNuclear poresNucleoplasmChromatinnuceolus

Acts as the control centre of the cell through the production of mRNA and protein synthesis

Retain genetic material of the cell (DNA / chromosomes)

Start the process of cell division

Chromatin DNA and associated proteins, chromatin

condenses into chromosomes when the cell divides.

nucleolus Manufactures ribosomal RNA and

assembles the ribosomes

Nuclear envelope Controls entry and exit of materials Outer membrane continuous with

endoplasmic reticulumNuclear pores

Passage of large molecules (mRNA) out of nucleus

Chloroplast envelope Entry and exit of substances

Stroma Enzymes for the light independent

stages of photosynthesisGrana (thylakoids/lamellae)

Light dependent stage of photosynthesisStarch grains

Temporary stores of carbohydrates

Double membrane Inner membrane folded into cristae

which provide a large surface areaMatrix

DNA, enzymes and ribosomes

Site of Krebs cycle and oxidative phosphorylation in aerobic respiration

Production of energy rich ATP molecules from carbohydrates

Membranes spreading through the cytoplasm of cells, continuous with the nuclear membrane

Enclose flattened sacs called cisternae Rough endoplasmic reticulum

Ribosomes present on outer surface of membrane

Smooth endoplasmic reticulum No ribosomes, tubular in appearance.

RER Provide LSA for synthesis of proteins Provides a pathway for the transport of

materials (esp. proteins) throughout the cell.

SER Synthesis, stores and transports lipids

and carbohydrates Contains lytic enzymes (liver cells)

Two types 80S – eukaryotic cells 70S – prokaryotic cells

Make up 25% of dry mass of cell

Important in protein synthesis

Stack of membrane bound, flattened sacks

Modifies and packages proteins Adds carbohydrates to proteins to form

glycoproteins Produces secretory enzymes

Secretes carbohydrates Transports, modifies and stores lipidsForms lysosomes

Spherical sac surrounded by a single membrane

Contains powerful digestive enzymes

Destroy foreign material inside or outside the cell. Breakdown material ingested by

phagocytic cells Release enzymes outside the cell Digest worn out organelles (autophagy) Autolysis break down cells after they

have died.

Structure Threads that extend from cell surface Made of nine sets of 3 microtubules

Function Move an entire organism Move material within an organism▪ E.g. cilia lining respiratory tract move mucus

towards the throat.

Structure 9 sets of microtubules in a circle 2 central microtubules

Function Movement▪ Tail of a sperm▪ Whole of unicellular organism

Hollow cylinders of microtubulesMicrotubules form spindle fibres for

nuclear divisionMaybe involved in formation of

microtubules that make up cells cytoskeleton

Structure Made of cellulose

Function Supports the cell▪ Cell turgor pressure

Similarities between plant and animal cells Make a list of the structures plant and

animal cells have in common Make a table of the differences between

plant and animal cells

Include all structures in plant and animal cells not just the ones observed through a Light microscope

explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement;

Cells contain a network of fibres made of protein, providing an internal framework.

Fibres can move organelles round within a cell. Microtubules

Move chromosomes around in cell division Move vesicles from endoplasmic reticulum to Golgi

apparatus ATP is used to drive some of these movements

outline the interrelationship between the organelles involved in the production and secretion of proteins

Instructions in DNA is nucleus Instructions copied onto mRNA mRNA moves to ribosome, where

protein is assembled Protein transported to Golgi apparatus Protein modified and packaged Protein moves in a vesicle to the cell

surface membrane Protein secreted.


Prokaryotes were probably the first forms of life on earth. Their heredity material (DNA) is not enclosed within a nuclear membrane. There are no membrane bound organelles within a prokaryotic cell.

The absence of a true nucleus only occurs in 2 groups. Bacteria Blue green algae (cyanobacteria)

Five structures, which are always present in a prokaryotic cell, are: cell wall, plasma membrane, cytoplasm,

ribosome, circular DNA

Copy and complete the following table

Include organelles, DNA, RNA and protein synthesis, ribosome, cell division, cell wall, cellular organisation.

prokaryotic Eukaryotic

organisms

Cell size

metabolism


organisms Bacteriacyanobacteria

Protista, fungi, plants, animals

Cell size 1 – 10 µm 10 –100 µm

metabolism Anaerobic and aerobic

Aerobic

organelles No membrane bound organelles

Nucleus, mitochondria, chloroplasts, RER, SER


DNA Circular DNA in cytoplasm

DNA organised into chromosomes bounded by nuclear envelope

RNA and Protein Synthesis

Synthesised in same compartment

RNA synthesised and processed in nucleusProtein synthesis in cytoplasm

Ribosomes 70S Type 80S Type

Cell Division Binary fission Mitosis or meiosis

Cell Membrane

Learning Objectives

outline the roles of membranes within cells and at the surface of cells

state that plasma (cell surface) membranes are partially permeable barriers

describe, with the aid of diagrams, the fluid mosaic model of membrane structure

describe the roles of the components of the cell membrane; phospholipids, cholesterol, glycolipids, proteins and glycoproteins;

outline the effect of changing temperature on membrane structure and permeability

Experimental work on plasma membrane Damage to cell membrane kills the cell Oil soluble substrates can penetrate

quickly => contains lipid Lipid solvents alter permeability

properties

Theory Monolayer? But water in contact with both surfaces,

bimolecular Proteins added to model to explain its strength

Davson and Danielli1935

Lipid bilayer coated on both sides with a layer of protein molecules

Calculated that thickness of membrane was about 7.5nm.

Phospholipid bilayer

Protein molecule

Singer and Nicholson 1972Fluid mosaic modelCell membranes have a consistency

like oil, with sideways movement of molecules or membrane. Fluid ▪ individual phospholipid and protein molecules

move around within their layer Mosaic▪ pattern produced by scattered protein

molecules when surface membrane is viewed from above.

Fluid Mosaic Model

A phospholipid bilayerTransmembrane and peripheral

proteinsCholesterolGlycoproteins Glycolipid

Cell Surface Membrane

Functions of the plasma membrane

Providing a partially permeable barrier

CompartmentalisationLocalising reactions in a cellTransport of solutesSignal transductionCell-cell recognition

Applying your knowledge questions

why can phospholipid molecules in a bilayer move only in the plane of the bilayer? Phosphate head can not pass through

the hydrophobic region in the centre of the bilayer

Applying your knowledge questions

Why do we describe cell membranes as partially permeable rather than semi-permeable? Different membranes are permeable to a

variety of substances and impermeable to a variety of others.

Semi-permeable suggests “half-permeable” which is unlikely to be the case in any membrane.

Roles of Components of Membrane

Phospholipid Can form sheets (bilayer) Form membrane bound compartments. Act as a barrier to most water soluble

substances


Cholesterol Helps regulate fluidity of membrane Stabilises phospholipid bilayer Prevent ions/polar molecules passing

through, important in myelin sheath around nerve cells.


Proteins Intrinsic proteins – span membrane Extrinsic proteins – embedded in one

half of membrane Channel forming proteins Carrier protein molecules


Glycolipids and Glycoproteins Short carbohydrate chains attach to lipids and

proteins Chains project into watery fluid surrounding

membrane, forming hydrogen bonds with the water, and increasing stability of membrane structure.

Receptor molecules – bind hormones and neurotransmitters, e.g. insulin receptors in liver and muscle cells

Antigens – allow cells to recognise each other e.g. white blood cells

Investigating Cell Membranes

Analysis of pigment leakage from beetroot cells

Two investigations Investigating the effects of temperature

on the cell membrane Investigating the effects of ethanol on

the cell membrane

Investigating the effects of temperature on the cell membraneRange of temperatures

0oC, 25oC, 50oC, 75oCFair test

List what you are changing List what you are keeping the same

Diagram of set upResults table (colorimeter reading)ConclusionsAnalysisEvaluation

Investigating the effects of ethanol on the cell membrane Range of ethanol concentrations

0%, 25%, 50%, 75% and 100% Fair test

List what you are changing List what you are keeping the same

Diagram of set up Results table (colorimeter reading) Conclusions Analysis Evaluation

Cell Signalling

Learning Outcomes

To explain the term “cell signalling”To explain the role of membrane-

bound receptors as sites where hormones and drugs can bind

Cell Signalling

Cells communicate with each other by signals

Cells must be able to detect various internal and external signals in order to co-ordinate the life processes of growth, development, movement and excretion.

Receptors can be Internal – e.g. steroid receptors External – e.g. insulin receptors

Signalling in animal cells

Signalling molecules fit into their receptors like keys into a lock

The shapes are complementary There are 3 main ways

Neurones send signals direct to target cells using neurotransmitters (e.g. synapse)

Hormones travel long distances in the blood Local hormones (e.g. histamine) stimulate cells

in adjoining cells

Hormones

Endocrine cells secrete hormones into the blood stream

Target cells have receptors for the hormone molecule

When the hormone binds to a receptor the cell responds

Insulin

The pancreas secretes insulin, which is large and water soluble

Insulin binds to receptor molecules on the cell surface membrane of liver and muscle cells

This increases glucose channels in the cell membrane

Cells uptake more glucose, which lowers the blood glucose levels

Local hormones

These only travel short distances to adjoining cells e.g. Histamine Cytokines▪ Stimulate lymphocytes to divide by mitosis

and produce antibodies▪ Stimulates phagocytes to become more

active

steroids

As steroids are fat soluble, their receptors sites are inside the cells

Medicinal drugs

Are complementary to the shape of receptor molecules Agonists ▪ mimic the effect of the signalling molecule

Antagonists▪ Block the receptors to stop the signalling

molecule from having any effect

Agonists

Salbutamol (ventolin) Mimics adrenaline to relax smooth

muscle in the bronchi

Drugs to treat schizophrenia mimic a natural neurotransmitter

Antagonists

Beta-blockers Which block receptors to prevent heart

muscle from increasing heart rate Help to reduce blood pressure

Hijacking cells

Some viruses can bind with receptors on the cell surface membrane HIV and helper T lymphocytes

Some poison can bind with receptors BOTOX – toxin binds with receptors on

muscle fibres and prevents them from working causing paralysis

Transport across boundaries

Learning Outcomes

explain what is meant by passive transport (diffusion and facilitated diffusion including the role of membrane proteins), active transport, endocytosis and exocytosis;

Learning Outcomes

explain what is meant by passive transport (diffusion and facilitated diffusion including the role of membrane proteins), active transport, endocytosis and exocytosis;

Exchange across the plasma membrane

The membrane provides an effective barrier against the movement of substances, however some exchange between the cell and the environment is essential.

Transport across membranes

Materials can move across cell membranes: Passively▪ Diffusion (simple or facilitated)▪ Osmosis

Actively▪ Active transport▪ Bulk transport

Diffusion

Net movement of molecules or ions from a region of high concentration to a region of low concentration

Occurs along a concentration gradient

Result = equilibrium (molecules or ions evenly spread out within a given space or volume)

Factors affecting the rate of diffusion Concentration gradient

Greater the difference in concentration the greater the rate of diffusion

Temperature At higher temperature kinetic energy particles

increases Diffusion is faster

Surface area Greater the surface area, more particles can

cross Increases rate of diffusion

Factors affecting the rate of diffusionNature of molecules or ions

Large molecules diffuse slower Non-polar molecules diffuse more easily The respiratory gases (CO2 and O2) are

small enough to diffuse quickly through the membrane.

Large, polar molecules (glucose and amino acids) and ions (Na+ and Cl-) cannot diffuse through the phospholipid bilayer

Facilitated Diffusion

Protein molecules exist in membranes to facilitate diffusion.

2 type of protein molecule Channel protein ▪ transmembrane protein that forms a tunnel

through the bilayer. Carrier proteins ▪ change shape to help molecules move into

and out of cells.

Facilitated Diffusion

Active Transport

Energy consuming transport of molecules or ions across a membrane against a concentration gradient, made possible by transferring energy from respiration.

Energy makes the carrier proteins change shape, transferring ions across the membrane.

Examples of active transport

Reabsorption in kidneysDigestion in gut

Helps absorb glucose from our intestinesLoad sugars into phloem Inorganic ion uptake in root hairs

Magnesium ions are in short supply in the soil but are needed for photosynthesis

Bulk transport

This is the method of transporting large quantities of materials into cells (endocytosis) or out of cells (exocytosis) Endocytosis - Engulfing of material by cell

membrane to form a endocytic vacuole.▪ 2 forms▪ Phagocytosis the uptake of solid material▪ Pinocytosis the uptake of liquid

Exocytosis - Process by which materials are removed from cells

Examples of bulk transport

Hormones released into bloodstream from endocrine glands

White blood cells engulf invading microorganisms by phagocytosis

In plant cells materials to build the cell wall are carried outside in vesicles.

OSMOSIS

Special type of diffusion involving water molecules

Example: Two solutions are separated by a

partially permeable membrane. Solute molecules are too large to pass through pores in the membrane, but water molecules are small enough.

What would happen if the membrane were not present?

Net movement of solute molecules from B to A by diffusion

Net movement of water molecules from A to B by diffusion

Equilibrium – concentrations of water molecules and solute molecules in A would equal that in B.

What will happen if the membrane is present?

What will happen if the membrane is present?

Solute molecules too large to pass through membrane

Water molecules pass easily from A to B Net movement of water from A to B until

equilibrium is reached, i.e. solution A has the same concentration of water molecules as solution B.

The level of liquid A will fall and the level of liquid B will rise

Equilibrium is brought about by the movement of water molecules alone.

Definition of osmosis

Water potential Ψ Tendency of water molecules to diffuse from

one place to another. Measured in kPa Pure water has a water potential of 0kPa

Osmosis Is the net movement of water molecules from a

region of high water potential to a region of low water potential (down a water potential gradient) across a partially permeable membrane.

Water potential

Highest water potential

0kPaPure water No solute

Lower water potential-50kPa

Dilute solutionSmall amount

of solute dissolved

Very low water

potential -500kPa

Concentrated solution

Large amount of solute dissolved

Decre

asin

g w

ate

r p

ote

ntia

l

Some Important Terms

Hypotonic a region of ▪ higher water potential.▪ Lower solute concentration

Hypertonic a region of ▪ lower water potential▪ Higher solute concentration

Isotonic a region where there are equal water potentials

on either side of a membrane.

Determining Water Potential in Potato tubers

Salt Soluntion(mol-1)

Starting Mass (g) Finishing mass (g) Change in mass (g)%age change in

mass

0.1

0.2

0.3

0.4

0.5

Osmosis in Red Blood Cells

Osmosis in Plant Cells

Important Terms

Turgid the term used to describe a plant cell

where the protoplast exerts a pressure on the cell wall.

Plasmolysed the term used to describe a plant cell

where the protoplast has shrunk away from the cell wall due to loss of water by osmosis.

Osmosis in red onion cells

Cell Division, Cell Diversity and Cellular

Organisation

OCR AS BiologyUnit F211: Cells, exchange

and transportModule 1: Cells

Time to think about things?

Define growthHow do organisms increase in size?How do organisms reproduce?

Cell Division

The answers to all of these questions link into cell

division!Cell Division allows for

reproduction and growth of organisms.

Learning Outcomes

state that mitosis occupies only a small percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information

Chromosomes

Are found in the nucleus of eukaryotic cells

Are made up of DNA and histone proteins Hold instructions for making new cells

Specific lengths of DNA are called genes The number of chromosomes in each cell

is characteristic of each species There are 46 chromosomes in humans

Daughter cells must contain a full set of chromosomes Before a cell divides the DNA of each

chromosome must be replicated

Structure of a chromosomes

ChromatidChromatid

A replica strand of DNA

Each one will end up in a different daughter cell

CentromereCentromere

Holds the two copies together.

Chromatin is supercoiled to form visible Chromatin is supercoiled to form visible chromosomes, this allows them to be moved chromosomes, this allows them to be moved around.around..

The Cell Cycledescribes the events that take place as one parent cell divides to produce new daughter cells which then each grow to full size.

M Nuclear division (mitosis) Cytokinesis (cleavage of cytoplasm)

Interphase G1▪ Biosynthesis – proteins are made and organelles

replicate,

S▪ Synthesis of new DNA▪ Replication of chromosomes

G2 - growth

The Cell Cycle (recap)

The cell cycle has 3 main phases Interphase▪ cell grows to normal size▪ carries out normal biochemical functions▪ DNA replication takes place

Nuclear division▪ mitosis, this has 4 stages; ▪ prophase, metaphase, anaphase and telophase

Cell division▪ cytoplasm divides by cytokinesis

Th

e C

ell C

ycle

Learning Outcomes

Recap state that mitosis occupies only a small

percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information

explain the meaning of the term homologous pair of chromosomes;

describe, with the aid of diagrams and photographs, the main stages of mitosis (behaviour of the chromosomes, nuclear envelope, cell membrane and centrioles);

Nuclear Division

looking at the Karyotype of a human male, you can see: Homologous pairs – each pair has

distinctive banding when stained. 22 pairs of autosomes 1 pair of sex chromosomes (female XX;

male XY)

Karyotype

Human body cells are diploid (2n), meaning that they have 2 sets of chromosomes. Human gametes are haploid (n), where n is the number of chromosomes in a single set

Learning Outcomes

describe, with the aid of diagrams and photographs, the main stages of mitosis (behaviour of the chromosomes, nuclear envelope, cell membrane and centrioles);

Mitosis

Nucleus of a cell divides resulting in two nuclei which are genetically identical to the parent nucleus.

4 stages Prophase Metaphase Anaphase Telophase

ProphaseChromosomes become visible and the nuclear envelope disappears

MetaphaseChromosomes arrange themselves at the centre (equator) of the cell.

AnaphaseChromatids migrate to opposite poles

TelophaseThe nuclear envelope reforms

Mitosis Pupil Activities

HANDOUTS Looking at the diagrams – identify the stage of

mitosis, and describe what is happening Bioviewers

Slide set 55 – Plant Mitosis▪ Read the information provided ▪ Make a line drawing of each cell (all 8 slides)▪ Write a description of each drawing you make

Microscopes Calculating the mitotic index Collect a worksheet and a prepared microscope

slide

As there are not enough slides for everyone to do

the microscope work – these activities can be completed in any order

Learning Outcomes

explain the significance of mitosis for growth, repair and asexual reproduction in plants and animals;

state that cells produced as a result of meiosis are not genetically identical (details of meiosis are not required);

Requirements of Nuclear Division

There are two requirements of nuclear division Growth (Mitosis); ▪ where a diploid zygote grows into a multi-

cellular adult, all daughter cells have the same number of chromosomes as the parent cell.

sexual reproduction (Meiosis); ▪ the number of chromosomes is halved so that

gametes are haploid

Human Life Cycle

Adult46

HaploidSperm

23

HaploidEgg23

Diploid Zygote

46

fertilisation

Meiosis

Chromosome number is halved so human gametes have 23 chromosomes

This reduction in chromosome number ensures that when gametes fuse to form a zygote (fertilisation) the diploid chromosome number is restored.

Meiosis

Learning Outcomes

outline, with the aid of diagrams and photographs, the process of cell division by budding in yeast;

Cell Division

In most cells, the nucleus divides first then the cytoplasm (cytokinesis).

This is mitosis and can be used for: Growth and repair Replacement of cells Asexual reproduction

In bacteria, cell division takes place by binary fission DNA replicates Cell divides

Cell division in yeast

Yeast is a single celled fungus It reproduces asexually by budding

Cell produces a swelling (bud) Nucleus divides into two – the bud gains

a nucleus The bud breaks off leaving a bud scar

Sometimes buds produce their own buds before separating.

Learning outcomes

To define the term stem cell Explain the meaning of the terms tissue,

organ and organ system; explain, with the aid of diagrams and

photographs, how cells are organised into tissues, using as examples squamous and ciliated epithelia, xylem and phloem

discuss the importance of cooperation between cells, tissues, organs and organ systems

Stem Cell

Stem cells are omnipotent or totipotent

The are cells which contain a full set of genetic information, and are capable of becoming any one of the different cell types found in a fully grown organism.

Stem Cells

There are a small number of stem cells found in adult mammals in the bone marrow, these are responsible for the formation of bone cells and blood cells.

Stem cells are currently being used in medical research.

Differentiation

Unspecialised cells which show totipotency include Stem cells in animals Meristematic cells in plants

These cells divide and then specialise, this is differentiation.

Differentiation and organisation

There is a physical limit to the size a single cell can reach, therefore multicellular organisms need specialised cells.

These specialised cells are organised into tissues which carry out a specific function.

Tissues are organised into organs.

Differentiation of cells

Cells differentiate in a number of ways, by changing: The number of a particular organelle▪ Muscle and liver cells contain many mitochondria

The shape of the cell▪ Red blood cells are a biconcave shape

Some of the cell contents▪ Red blood cells do not contain a nucleus

Differentiation means to specialise to carry out a particular role or function.

Examples of specialised cells

Erythrocytes Neutrophils

Sperm Root hair cells

Lose their nucleus, mitochondria, Golgi apparatus and RERContain Haemoglobin

Erythrocytes

Granular cytoplasm due to large numbers of lysosomes

Neutrophils

Energy for movement of the undulipodium comes from the large number of mitochondria. Head contains specialised lysosomes

Sperm

Hair-like extension, to increase the surface area for water absorption.

Root hair cells

Structure of specialised cellsTry to write out the specific function of each specialisation

Tissues, organs and systems Tissue

a group of similar specialised cells in a many celled organism, that carries out a specific function or several related functions

Organ group of different tissues forming a distinct

structure and functioning together▪ animal – lungs, heart, kidneys▪ plant – roots, stems, leaves

System collection of organs with a particular function▪ cardiovascular and digestive systems

Tissues

A tissue is a group of similar, specialised cells which carry out a specific function, or several related functions. Animal tissues ▪ squamous and ciliated epithelium

Plant tissues▪ Xylem and phloem

Animal Tissues

Tissues that form sheets covering surfaces are called epithelial tissues, epithelial tissues are one cell thick and rest on a basement membrane (a network of collagen and glycoproteins), which holds the cells in position.

Two examples of animal tissues are squamous and ciliated epithelium.

Ciliated Epithelium

This tissue is found lining the ends of the bronchioles in the lungs.

Squamous Epithelium

This tissue covers many surfaces in the human body including the inner lining of cheeks and lining the walls of the alveoli in the lungs.

In the alveoli, the thinness of cells allows rapid diffusion of gases between alveoli and blood.

Squamous Epithelium

Plant Tissues

Examples of plant tissues include xylem and phloem, which are transport tissues in plants. Xylem transports water and ions,

phloem transports sugars and other compounds made by plants.

Tissues can be presented in plan diagrams, plan diagrams DO NOT show any individual cells.

Plan Diagrams – dicotyledonous leaf

Plan Diagrams - dicotyledonous leaf

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OCR AS Biology Unit 1: Cells, Exchange and Transport