3.2- Cells Flashcards
What is the cell theory?
-All living organisms are made up of one or more cells.
-Cells are the basic functional unit (i.e. the basic unit of structure and organisation) in living organisms.
-New cells are produced from pre-existing cells.
-Cell theory is accepted by ALL scientists!
What is the microscopy equation?
magnification= image size/ specimen size
What are the units of measurement for microscopy?
metre x 1000 = mm
mm x 1000=micrometre
micrometre x 1000= nanometre
Resolution definition?
The minimum distance apart at which 2 seperate objects can be distinguished.
Artefact definition?
Something observed that is only there due to preparation techniques- eg air bubbles.
Magnification definition?
How much bigger the image is than the original object.
What is an eyepiece graticule?
Glass disc with 100 subdivisions, we do not know the length.
What do we do before using an eyepiece graticule?
We have to calibrate the graticule as each objective lens will magnify to a different degree so we cannot use the scale directly.
Have to convert graticule units into real units
How do we calibrate an eyepiece graticule?
You would use a stage micrometer- another slide which is 1mm and has 100 subdivisions- each division is 0.01mm
So how do we measure the size of a specimen?
Line up 1 of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.
Count number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.
Divide one micrometre measurement (eg 0.1mm) by the n of eyepiece divisions in the same length.
How many µm would each graticule division have if there are 35 divisions in 200µm of the stage micrometer?
length of micrometer in µm/ number of divisions
200 µm / 35 graticule divisions = each division is 5.7 µm
What is cell fractionation?
A method used to isolate different organelles so they can be studied.
How are the cells prepared?
In a cold, isotonic, buffered solution.
Cold- to reduce enzyme activity as when cell breaks open enzymes are released- could damage organelles.
Isotonic- Solution has same water potential as organelles to prevent osmosis as this could cause organelles to shrivel/ burst.
Buffered- solution has pH buffer(stays neutral) to prevent denaturing of the enzyme/protein if the pH were too high or low.
What is 1st step of cell fractionation?
Homogenisation.
Cell must be broken open (homogenised) using a blender/ homogeniser. Cells are blended in cold, isotonic, buffered solution.
Solution is then filtered through gauze to remove any large cell/tissue debris.
What is 2nd step of cell fractionation?
Ultracentrifugation.
Filtered solution is spun at different speeds in centrifuge, organelles separate according to their densities.
What is process of differential centrifugation?
1) Centrifuge spins at lowest speed and centrifugal forces cause organelles to form pellets. Most dense organelles form 1st pellet and move to bottom.
2) Fluid at top of tube (supernatant) is removed, leaving behind the sediment/pellet of the organelle at bottom.
3) Supernatant transferred to another tube and spun in centrifuge at faster speed than before.
4) Process is repeated, with most dense organelle forming sediment, supernatant being spun at faster speed than before.
What is the order that the organelles separate?
Nuclei, Chloroplasts, Mitochondria, Lysosomes, Endoplasmic Reticulum, Ribosomes.
(Naughty Chunky Monkeys Like Eating Red Raspberries!)
How does a light microscope work?
Light is focused using glass lenses, it relies on the light being able to pass through the specimen.
Regions that absorb more light appear darker in image.
Advantages + disadvantages of light microscope.
Advantages- easy to use, cheap, show the true colour of the specimen, can use live specimen.
Disadvantages- low resolution due to longer wavelength of light, low magnification (max 1250X)
2 structures in eukaryotic cell that cannot be identified using an optical microscope?
Lysosomes
Ribosomes
What are the 2 types of electron microscope?
Scanning Electron Microscope and Transmission Electron Microscope.
How does SEM work?
It directs a beam of electrons at a specimen.
It creates an image based on the electrons that are reflected.
It is focused using electromagnets to create a 3D image.
Advantages + disadvantages of SEM?
Advantages- much higher resolution than light microscope (1nm), detailed images of surface structures, high mag (300,000X).
Disadvantages- very expensive, extensive training required, samples must be dead (vacuum, stain), false colour/ B+W image.
How does TEM work?
It directs a beam of electrons at a specimen.
It creates an image based on the electrons that are absorbed.
It is focused using electromagnets to create a 2D image.
Why can detail not be seen using an optical microscope?
Due to the optical microscope using light: light has a longer wavelength so it has a smaller resolution.
Advantages + disadvantages of TEM.
Advantages- much higher resolution than light microscope (1nm), detailed images of interior structures, highest magnification (500,000X).
Disadvantages- very expensive, extensive training required, samples must be dead (stain or vacuum), false colour/ black+white image.
Structure and function of cell-surface membrane?
partially permeable membrane found on surface of animal cells and some organelles like mitochondria and nucleus.
Mainly made of lipids and proteins-made up of a lipid bilayer, which consists of two layers of phospholipid molecules.
-Regulates movement of substances in and out of the cell
-Has receptor molecules so can easily respond to chemicals like hormones
Structure of the nucleus?
Outer nuclear envelope- double membrane which contains pores.
Nuclear pores- control movement of materials between nucleus and cytoplasm
Nucleoplasm- jelly like material which fills the nucleus.
Chromatin- form of DNA found in the nucleus when chromosomes are NOT dividing.
Nucleolus- small spherical body involved in making ribosomes- rNA production. (mini nucleus)
Function of the nucleus?
Control centre for cell through the production of proteins
Contains the genetic code for each cell.
Makes ribosomal RNA and ribosomes
Structure and function of mitochondria?
Structure- oval shaped, has a double membrane. Inner membrane folded to form cristae (bumpy parts of membrane), matrix inside mitochondria contains enzymes.
Function- site of aerobic respiration(converts energy from food into ATP)
-cristae provides large SA for some enzymes to be embedded into inner membrane
-found in large numbers in metabolically active cells+cells which actively transport.
Structure of chloroplasts (plants+algae)?
Has a chloroplast envelope- double plasma membrane which is selective on what can enter/leave the chloroplast.
A stack of disc-like structures called thylakoids- is called a granum. Grana are connected to each other by lamellae.
Fluid filled stroma contains enzymes for photosynthesis.
Function of chloroplasts?
1st stage of photosynthesis (light absorption) occurs in grana.
Granal membranes provide large SA- for attachment of chlorophyll, electron carriers, and enzymes that carry out 1st stage of photosynthesis.
2nd stage of photosynthesis ( synthesis of sugars) occurs in the stroma.
Thylakoids contain photosynthetic pigment chlorophyll.
Chloroplasts contain DNA and ribosomes- can easily manufacture some proteins needed for photosynthesis.
Structure of Golgi apparatus+ golgi vesicles?
Stack of folded membranes forming cisternae- more curved than ER. Secretory vesicles pinch off from the cisternae.
Functions of Golgi apparatus?
-Add carbohydrates to proteins to form glycoproteins
-Produce secretory enzymes
-Secrete carbohydrates (eg- those used in making plant cell wall)
-Transport, modify and store lipids
-Produce lysosomes
-Can label molecules for their destination- eg by adding a receptor
-Transport finished products to cell surface membrane in golgi vesicles where they fuse with membrane and contents are released.
Structure and function of lysomes?
Sacs of digestive enzymes formed by golgi apparatus
-Hydrolyse phagocytic cells
-Completely break down dead cells- autolysis
- Release enzymes to outside of cell to destroy materials- exocytosis
-Digest worn out organelles for reuse of materials.
Structure and function of ribosomes?
Small organelles made of 2 subunits- protein and rRNA joined together. 80S- larger ribosomes found in EUKARYOTIC cells. 70S- smaller ribosomes found in PROKARYOTIC cells.
-Site of protein synthesis
Structure and function of rough endoplasmic reticulum (RER)?
A 3D system of folded membranes called cisternae.
The cisternae in RER have ribosomes attached.
-The RER folds and packages proteins and sends them to the Golgi Apparatus
-Protein synthesis occurs in RER, provides pathway to transport materials.
Structure and function of smooth endoplasmic reticulum (SER)?
A 3D structure of folded membranes called cisternae.
-Synthesises, stores (in sacs), and transports vital lipids and carbohydrates.
Structure and function of cell wall (plants, algae, fungi)?
Plants: made of microfibrils of the polymer cellulose.
Fungi: made of chitin, a nitrogen-containing polysaccharide.
Provides structural strength for the cell.
Structure and function of cell vacuole (plants)?
Fluid-filled sac surrounded by single membrane called a tonoplast.
-Makes cell turgid by pushing out, providing structural support
-Temporary store of sugars and amino acids
-Pigments may colour petals to attract pollinators
Structure and function of cytoplasm?
Contains the organelles, most chemical reactions occur in cytoplasm.
How do prokaryotic cells differ from eukaryotic cells?
-They are smaller than eukaryotic cells.
-They have no membrane-bound organelles.
-They have smaller, 70S ribosomes.
-Their cell wall is made of murein (a glycoprotein) not cellulose.
-They have no nucleus- there is a single circular DNA molecule which is free in the cytoplasm.
What extra structures may prokaryotic cells contain?
They may also contain: plasmids (small loops of DNA which only contain a few genes) a capsule surrounding the cell to stop the bacteria from drying out (helps to cover antigens on the outside, protects bacteria from immune system, flagella/flagellum which help with movement.
What can plasmids contain?
Antibiotic- resistant genes can be found in the plasmids.
What are viruses?
Acellular, non living organisms which cannot reproduce independently.
NOT living organisms!!!!!
What is the typical structure of a virus?
All viruses contain genetic material (DNA or RNA) which is contained inside a protein structure called a capsid.
On the surface of the virus, there are attachment proteins which allow the virus particle to attach to and enter the host cell.
In some viruses, the capsid can be surrounded by a lipid envelope formed by the host cell membrane.
How may viruses be able to infect other species?
A mutation in their viral DNA/RNA could lead to a change in tertiary structure of the viral attachment protein allowing the virus to bind to receptors of other species.
How do viruses reproduce?
Viruses cannot reproduce independently, they must reproduce within a host cell.
The virus particle attaches to the surface of a host cell, then it enters the host cell. It uses the host cells enzymes to produce copies of itself. The virus particles leave the host cell and can go on to infect new host cells.
Adaptations of palisade cell in leaf?
Large number of chloroplasts: present in cytoplasm to maximise absorption of light for photosynthesis.
Tall + thin shape: allows light to penetrate deeper before encountering another cell wall (cell walls absorb and reflect light), many cells can be densely packed together.
Located right below the epidermis and the cuticle- carries out photosynthesis to produce glucose and oxygen.
Adaptations of root hair cell?
Large SA: increases the rate of absorption of water and minerals.
Large permanent vacuole: speeds up movement of water by osmosis from soil across root hair cell.
Many mitochondria: transfer energy needed for active transport of mineral ions into root hair cells.
Adaptations of xylem cell?
No organelles or cytoplasm: more space inside vessel for transporting water.
Walls contain pits: allow water and mineral ions to move in and out of the vessel.
Wall contains lignin: strengthens xylem vessel and provides structure+support to the plant.
Dead cells: do not interfere with the mass flow of water.
One way flow system: allows continuous upward flow of water driven by transpiration stream.
Adaptations of phloem cell?
Living cells: transport of food through sieve tube elements requires active transport.
Cells are joined end-to-end, contain holes in end cell walls(sieve plates): this forms tubes which allow sugars and amino acids to flow easily through transpiration.
Specialised sieve tubes: have no nuclei, are specialised for transport.
Companion cells: attached to each sieve tube providing the energy for the transport of substances in the phloem- have many mitochondria and ribosomes.
What is gene expression?
All cells have same genetic info.
Only a few genes are switched on (expressed) in a given cell.
These are the genes that give the cell its required characteristics.
Organisation of multicellular organisms?
cells —> tissues —> organs —> organ systems
What are tissues?
Similar cells that are aggregated together (clustered together) to perform a specific function.
These are dependant on one another.
Tissue examples?
1) Squamous epithelium tissue- single layer of flat cells lining a surface: found in skin, or alveoli of lung. Selective about which materials can diffuse in or out.
2) Phloem tissue- transports sugar around a plant. Each sieve cell has end walls with holes so sap can easily move through them. End wall = sieve plate
3) Xylem tissue- transports water around the plant, and supports the plant. Contains xylem vessel cells and parenchyma cells.
What are organs?
An organ is a structure that contains at least 2 different types of tissue functioning together for a specific purpose.
Organ examples?
1) The lungs- made of:
-squamous epithelial tissue which surrounds the alveoli (where gas exchange occurs),
-fibrous connective tissue which contains fibres that help force air back out of lungs when exhaling,
-blood vessels- capillaries which surround the alveoli.
2) The leaf-made of:
-lower epidermis- contains stomata (pores) which let air in or out for gas exchange.
-upper epidermis- covered in waterproof waxy cuticle to reduce water loss.
-spongy mesophyll- space for gas to circulate.
-palisade mesophyll- most photosynthesis occurs here.
-xylem- carries water to the leaf.
-phloem- carries sugar away from the leaf.
What are organ systems?
Organs that work together as a single unit to perform a particular function.
Organ system examples?
1) Circulatory system- allows transport of gases and other substances around the body. Blood vessels carry blood to tissues, heart pumps blood around body, oxygen from lungs to tissues and organs.
2) Respiratory system- brings O2 into the body and removes CO2. Trachea allows air flow, bronchi carry air into lungs, gas exchange occurs in lungs.
3) Shoot system in plants- includes flowers for sexual reproduction, leaves which are site of photosynthesis, buds which are growing regions and stems for support.
What is the cell cycle?
A regular cycle of division separated by cell growth.
What are the 3 stages of the cell cycle?
Interphase, Nuclear division and Cytokenisis
What happens during interphase?
G1, S and G2.
G1= Gap phase 1: cell grows in size, all organelles are doubled to prepare for the 2 new cells containing the same amount of DNA and being the right size and ATP is produced.
S= Synthesis: The DNA is replicated.
G2= Gap phase 2: cell grows again, DNA replicated is checked for potential mutations (cell is destroyed if there are mutations), proteins needed for division are made, centrioles replicated.
What happens during nuclear division?
Mitosis or meiosis: one round of division for mitosis, the cell splits into 2 to produce 2 genetically identical daughter cells.
What happens during cytokenisis?
Cell division- the cytoplasm and cell membrane divide to produce 2 new cells (mitosis) or 4 new cells (meiosis).
How is cell division represented on logarithm graphs?
You use log when there is a large range of data so it is easier to plot and read.
log(value)
reverse log = 10^log
What are homologous chromosomes?
Pair of chromosomes with the same gene loci that determine the same features.
Homologous chromosomes carry the same genes but are not genetically identical- why?
They carry different alleles.
What are sister chromatids?
2 different copies of the same chromosome held together at the centromere.
How to remember the cell cycle + which part is mitosis?
IIIIIIIIIIIIIIPMAT= Interphase, prophase, metaphase, anaphase, telophase.
(PMAT) is mitosis.
What happens during prophase?
The chromosomes condense (they become shorter and visible) and the nuclear envelope disintegrates. The centrioles move to opposite poles of the cell and form spindle fibres.
NO NUCLEOLUS
Plants do contain spindle fibres/ apparatus but do NOT have centrioles!
What happens during metaphase?
The centrioles are at opposite poles and their spindle fibres attach to the centromere of the sister chromatids.
Chromosomes released from the nucleus line up along the equator of the cell.
What happens during anaphase?
The spindle fibres retract back into their centrioles, putting tension on the centromere holding the sister chromatids together.
The centromere divides in 2 and the chromatids are pulled to opposite poles of the cell. This requires energy in the form of ATP provided by respiration in mitochondria. V shape of chromosomes shows that they have been pulled apart at their centromeres.
What happens during telophase?
Chromosomes are at opposite poles, becoming long and thin again (CANT SEE THEM).
Spindle fibres disintegrate, nuclear envelope starts reforming around each group of chromosomes.
2 nuclei may be visible.
What happens during cytokenisis?
Cell division- the cytoplasm splits to separate the 2 cells, they enter interphase again and the cycle restarts.
Why is mitosis important?
For growth of organisms as they increase in the number of cells.
To replace damaged cells which can repair tissue/organs.
What is the mitotic index?
The ratio of the number of cells undergoing mitosis to the total number of cells.
How would you calculate mitotic index?
number of cells in mitosis (PMAT) /
total number of cells x100
How to calculate how many cells there will be after a certain amount of divisions?
2 to the power of however many divisions there are as the number of cells doubles for each cycle.
Eg- 4 divisions= 2^4= 16 cells
In mitosis, what happens to the DNA mass and the chromosome number?
The DNA mass halves and the chromosome number stays the same.
What is the role of centromeres in mitosis?
They hold sister chromatids together, they attach chromatids to the spindle, allowing the chromatids to move to opposite poles.
