4.1.1 Cell structure - Hart School...4.1.3 Transport in cells Diffusion is the spreading of the...
Transcript of 4.1.1 Cell structure - Hart School...4.1.3 Transport in cells Diffusion is the spreading of the...
4.1.1 Cell structure
Functions of organelles
Organelle Function Plant or animal
NucleusContains genetic material, which controls
the activities of the cellBoth
CytoplasmMost chemical processes take place here,
controlled by enzymesBoth
Cell membraneControls the movement of substances into
and out of the cellBoth
Mitochondria Most energy is released by respiration here Both
Ribosomes Protein synthesis happens here Both
Cell wall Strengthens the cell Plant ONLY
ChloroplastsContain chlorophyll, absorbs light energy
for photosynthesisPlant ONLY
Permanent vacuole
Filled with cell sap to help keep the cell turgid
Plant ONLY
All living things are made up of cells. The structures of different types of cells are related to their functions.
Prokaryotic cellsBacteria
Comparing Prokaryotic and Eukaryotic
Prokaryotic Eukaryotic
No membrane bound nucleus Membrane bound nucleus
DNA is single stranded DNA is double stranded
May contain plasmids Do not contain plasmids
Smaller Larger
Eukaryotic cells
Standard form
Keywords
Keyword Definition
Unicellular Single celled organisms
Multicellular Organisms that consist of more than one cell
Prokaryote A unicellular organism that has no membrane bound organelles
Eukaryote A cell from any organism that contains membrane bound organelles, can be multicellular or unicellular.
Organelle Structures found within cells that have specialised functions
Membrane bound organelle
Organelles found within cells that have specialised functions and are surrounded by a plasma membrane e.g chloroplast, mitochondria, nucleus.
4.1.1 Cell structure Cells are specialised for a particular function. Structure helps them to carry this function out.
Specialised Cells
Cell Diagram Function Adaptations
Sperm cell Transport the male DNA to the female DNA.
Long tail – to swim.Lots of mitochondria – for energy.
Enzymes in head – to digest egg cell membrane
Nerve cell To carry electrical signals from one part of the body to another.
Long – to cover distance.Branched connections – to connect to other nerve cells.
Muscle cell To contract quickly. Long – so that they have space to contract.Lots of mitochondria – to generate energy for the contraction.
Root hair cells
To absorb mineral ions and water from the soil.
Long hairs – to stick into soil.Big surface area – to absorb more water and mineral ions.
Xylem cells To transport water in plants. Hollow in the centre – to allow water to flow through.
Phloem cells
To transport food in plants. Very few subcellular structures – to allow food to pass through.
Cell differentiation• Differentiation is the process by which a cell changes to become
specialised for its job.• As cells change, they develop different subcellular structures and
turn into different types of cells.• In most animal cells, cell differentiation mostly occurs when the
baby develops in the womb• Plant cell contain meristem tissue at the roots, buds, shoots and
tips and these retain the ability to differentiate throughout the life of the organism
• The cells that differentiate in mature animals are mainly sued for repair and replacing cells (e.g. skin or blood cells).
• Differentiation is caused by genes being switched on and off.• Undifferentiated cells are called STEM CELLS, and can give rise
many more cells of different types from which certain other cells
can arise from differentiation.• In some countries stem cell research is banned. In the UK it is
allowed as long as it follows strict guidelines
Arguments for and against the use of STEM cells
For Against
Adult Stem cells come from bonemarrow and can replace faulty blood
cells.
Adult stem cells can only differentiate into a small number of different cells so
cannot treat all illnesses
Embryonic stem cells could replaces faulty cells in sick people and help cure
disease. E.g diabetes
Embryonic stem cells shouldn’t be used as each embryo is a potential human
life which has to be destroyed.
Embryos are usually from fertility clinics, they are embryos not used in IVF
Adult stem cells have to be removed during an operation which is painful
Therapeutic cloning – embryo could be made to have the same genetic
information as the patient so they wouldn’t be rejected by the body
The use of stem cells has potential risks such as transfer of viral
Infection.
4.1.1 Cell structure
𝑚𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 =𝑠𝑖𝑧𝑒 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒
𝑠𝑖𝑧𝑒 𝑜𝑓 𝑟𝑒𝑎𝑙 𝑜𝑏𝑗𝑒𝑐𝑡
Microscopes let us see things we cannot see with the naked eye.
Comparison of light and electron microscopes
Light microscopes Electron microscopes
Use light and lenses to form an image of the specimen and magnify it.
Use electrons instead of light to form an image.
Can see individual cells and larger subcellular structures (e.g. nuclei).
Can see smaller structures in more detail (e.g. ribosomes, plasmids and
the internal structures of mitochondria and chloroplasts)
Lower resolution, due to light having a longer wavelength.
Higher resolution, due to electrons having a shorter wavelength.
Lower magnification. Higher magnification.
Can see living samples Samples must be dead
Resolution – the ability to distinguish between two points, the better the resolution the more detail can be seen in an image
Looking at your slide (using a light microscope)1. Clip slide onto stage.2. Select lowest-powered objective lens (lowest magnification).3. Use the coarse adjustment knob to move the stage up to just below
the objective lens.4. Look down the eyepiece. Use the coarse adjustment knob to move
the stage downwards until it is roughly in focus.5. Adjust the focus with the fine adjustment knob until you get a clear
image.6. If you need greater magnification, swap to a higher-powered
objective lens.
Converting Units
cm mm µm nm
x 10 x 1000 x 1000
÷ 10 ÷ 1000 ÷ 1000
Calculating magnification from an image
• Measure the line on the image in mm• Multiply the measurement by 1000• Divide by the actual size - this will be given in the information
Calculating actual from an image
• Measure the line on the image in mm• Multiply the measurement by 1000• Divide by the magnification - this will be given in the information
Calculating magnification from a scale bar
• Measure the scale bar in mm• Multiply the measurement by 1000• Divide by the actual size - the number underneath the scale bar.
Preparing a microscope slide
STEP EXPLANATION
Add a drop of water to the slide Create a seal between the slide and cover slip, stops sample drying out
Place a thin piece of the tissue to be viewed on the drop of water
The tissue needs to be thin to allow light to pas through it
Stain the tissue This allows structures in the tissue to be seen more easily
Place a cover slip gently on top of the tissue
This creates a seal between the tissue, slide and cover slip preventing bubbles which would obscure the image.
Magnification – The degree to which we make an image look larger than it actually is
4.1.2 Cell division
MITOSIS cell division for growth and repair of cells (produces clones).
1. Parent Cell – Chromosomes condense become visible
2. Chromosomes make identical copies of themselves (replicate).
3. The chromosomes line up along the centre of the cell
called the equator.
4. The chromosomes split and one set of chromosomes are
pulled to each end of the cell.
5. The cytoplasm splits and the cell membrane starts to form around each of the new cells
6. Two new daughter cells withidentical chromosomes to the
parent cell. The cells are diploid.
Genetic information is in the nucleus of cellsInside the nucleus are chromosomes made up of DNA –BODY CELLS have two sets of chromosomes (diploid) ,
SEX CELLS (gametes) have one set of chromosomes (haploid) in humans body cells 46 chromosomes (23 pairs), sex cells (sperm/egg) 23 single chromosomes.
Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.• Rare species can be cloned to protect from extinction.• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
The cell cycle describes the stages which cells go through to divide. There are 3 stages: 1. Cell growth to increase the number of organelles such
as cytoplasm and mitochondria2. DNA replication, where the amount of DNA doubles3. Mitosis where the DNA and cell contents divide into 2.
• Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature.
• Bacteria can be grown in a nutrient broth solution or as colonies on an• agar gel plate.
Microorganisms can be grown in the lab
• A culture medium (agar) used containing an energy source (carbohydrate) and minerals.
• Petri dishes and agar are sterilised before use to kill microorganisms.
• Inoculating loops used are sterilised by heating in a Bunsen flame
• The inoculating loop is used to transfer microorganisms from the sample to the agar plate
• At all times equipment is kept near a Bunsen flame to draw any airborne microorganisms into the flame to ensure there is no contamination
• Lid of the Petri dish should be sealed with two pieces tape to stop microorganisms getting in (must not be fully sealed so oxygen can get in) .
• In school petri dishes incubated at 25°C reduces risk of growth of pathogens that might be harmful to humans.
Culturing microorganisms – required practical
• Agar inoculated with BACTERIA.
• Paper discs containing antiseptics and antibiotics placed on bacteria using sterilised forceps
• Water DISK used as a CONTROL.
• Agar plate is sealed using two pieces of tape
• Agar is incubated for 24-48 hours
• If bacteria don’t grow around the disk then it is effective at killing bacteria.
• Area where bacteria don’t grow is called ZONE OF INHIBITION
4.1.3 Transport in cells
Diffusion is the spreading of the particles of a gas or liquid, resulting in a net movement of particles from a region where they are of a higher concentration to an area of lower concentration.
Substances may move into and out of cells using different processes.
Factors which increase the rate of diffusion:• A bigger difference in concentrations• A higher temperature• A bigger surface area (of the membrane).
A single-celled organism has a relatively large surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs
of the organism.
In multicellular organisms, surfaces and organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by:• having a large surface area• having a membrane that is thin• having an efficient blood supply (in animals)• being ventilated (in animals).
Surface area = length x width= (4 x 4) x 2+ (4 x 2 ) x 4 = 64 cm2
Volume = length x width x height= 4 x 4 x 2 = 32 cm3
Surface area to volume ration = 64:32 (2:1)
Examples of diffusion
Part Function Adaptation
Lungs (alveoli)
To exchange oxygen and
carbon dioxide.
• Large surface area.• Moist lining.
• Very thin walls.• Good blood supply.
Smallintestine
(villi)
To pass digested food into the bloodstream.
• Single layer of surface cells.• Very good bloody supply.
Leaves in plants
Exchange carbondioxide and
oxygen.
• Flattened shape (increased area).• Air spaces in leaf.
• Guard cells to open and close stomata.
Gills in fish
To exchange oxygen and
carbon dioxide.
Gill filaments (big surface area).Lamellae on gill filaments.Lots of blood capillaries.
Large concentration gradient (due to direction of blood flow).
OSMOSIS is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of
lower water concentration.
• A partially permeable membrane has very small holes in it so only tiny molecules (e.g. water can pass through).
• The water molecules pass in both directions because they move randomly.
• Because there are more water molecules on one side than on the other, there is a steady net flow of water into the region with fewer water molecules (more concentration sugar solution).
• You can place potato cylinders in different sugar solutions (one should be pure water and one very concentrated and some in between).
• You measure the mass of the potato cylinder, place it in the sugar solution for 24 hours and then measure the mass after (must be dry).
• If the mass has increased – water has been taken in by osmosis.• If the mass has decreased – water has been given out by osmosis.
IV – concentration of sugar solution.DV – mass of potatoCV – volume of solution, temperature, time, type of sugar etc.
ACTIVE TRANSPORT - Active transport is the movement of a substance against a concentration gradient (from low to high), using energy from respiration.
Root hairs in plants take in minerals using active transport.
Active transport happens in the gut
Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration
of nutrients in the blood.This happens when diffusion cannot occur.
Type of solution
Description Effect on animal cell Effect on plant cells
Hypotonic Solution surrounding the cell contains less solute than inside the cell
Water from the solution surrounding the cell enters the cell. The mass of the cell increases. Eventually the cell bursts. This is called lysis.
Water from the solution surrounding the cell enters the cell. The mass of the cell increase. Eventually the cell becomes turgid as the cell wall supports the cell and prevents bursting
Isotonic Solution surrounding the cell has the same solute concentration as the solution inside the cell
No overall net movement in or out of the cell. This is the state the cell is found in normally.
No overall net movement in or out of the cell.
Hypertonic Solution surrounding the cell contains more solute than inside the cell
Water from cells leave to surrounding solution. The mass of the cell decreases. The cell shrivels. This is called crenation.
Water from cells leave to surrounding solution. The mass of the cell decreases. The cell shrivels and becomes flaccid and eventually becomes plasmolysed.