ocr biology

what are the different parts of a light microscope

(see diagram)

how do light microscopes work

-visible light is passed through a specimen

-refracted through two lenses (objective and eyepiece lenses)

why do microscopy specimens need to be stained

-allows the specimen to be seen under the microscope

-different cells/organelles to be distinguished

how are specimens prepared to be viewed under a light microscope

-cut into very thin sections,

-laid flat on a glass slide

-stains added

-glass cover slip is added from an angle so air is not trapped underneath

-slide is placed on stage under lowest power lens and focused before higher power lenses can be used

how do you convert from m->mm->um->nm

x1000->x1000->x1000

how do you convert nm->um->mm->m

/1000->/1000->/1000

define magnification

the degree to which the size of an image is larger than the object itself

define resolution

the ability of a microscope to distinguish between two points (the amount of detail)

what is the formula for magnification

I = A x M (image size = actual size x magnification)

how do you prepare a dry mount

take a thin slice of the specimen and place it in the middle of a clean slide using tweezers then add a cover slide

how do you prepare a wet mount

place specimen on microscope slide and add a drop of distilled water, then add the cover slip from an air to prevent air bubbles getting trapped

how should scientific diagrams be drawn

-title,

-magnification

-smooth

-continuous lines

-no shading

what are the two types of graticule (microscope ruler)

eyepiece and stage/slide graticules

how do you calibrate an eyepiece graticule

-Line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece

-Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale

-Each division on the micrometer is 10μm, so this can be used to calculate what one division on the eyepiece graticule is at the current magnification

describe a light microscope

-uses light focussed by glass lenses,

-image can be viewed directly

-staining of specimen is required

describe a scanning electron microscope

electrons are reflected by specimen

uses electrons focussed by electromagnetic lenses,

cannot use live specimens

describe a transmission electron microscope

-higher density parts absorb more electrons and appear darker,

-uses electrons focussed by electromagnetic lenses in vacuum

-image is seen on a fluorescent screen

what are the advantages of a light microscope

-inexpensive,

-portable,

-can use living specimens,

-easy to use

what are the disadvantages of a light microscope

-low magnification and resolution,

-specimens need staining

what are the advantages of a scanning electron microscope

-can take 3D images, -high magnification and resolution

what are the disadvantages of a scanning electron microscope

-large,

-expensive,

-needs training to use

-dead

-complex staining method

what are the advantages of a transmission electron microscope

-highest magnification and resolution

what are the disadvantages of a transmission electron microscope

-large

-expensive

-needs training to use,

-specimen must be dead

-specimen must be stained

-must be v thin

which is the only type of microscope that can produce 3D images

scanning electron microscope

what are organelles

-small structures within cells,

-each of which has a specific function

what are eukaryotes

-cells which have a nucleus and other membrane bound organelles

what is the ultrastructure of a cell

-the fine detail of the structure within cells (viewed with an electron microscope)

which organelles are found in animal cells but not in plant cells

-centrioles

-lysosomes

which organelles are found in plant cells but not animal cells

-cell wall,

-permanent vacuole

-chloroplasts

what is the function of the plasma (cell surface) membrane

-regulates the movement of substances into and out of the cells

-has receptor molecules so can respond to chemicals like hormones

what is the function of the cell wall

support and protect the cell

what is the function of the nucleus

-controls the cells activities by controlling the transcription of DNA

-pores allow substances to move between the nucleus and cytoplasm,

-the nucleolus makes ribosomes

what is the function of the permanent vacuole

-stores nutrients

-water

-waste

what is the function of lysosomes

contain digestive enzymes that break down waste material (e.g. pathogens)

what is the function of ribosomes

site of protein synthesis

what is the function of the rough endoplasmic reticulum

makes and processes proteins

what is the function of the smooth endoplasmic reticulum

synthesises and processes lipids

what is the function of vesicles

-to transport molecules into, out of, and around a cell between organelles

-formed by the golgi apparatus/ER/cell surface

what is the function of the golgi apparatus

makes and packages proteins and lipids (also makes lysosomes)

what is the function of mitochondria

site of aerobic respiration

produce ATP

what is the function of chloroplasts

where photosynthesis occurs

what is the function of centrioles

-involved with the separation of chromosomes during cell division

what is the the cytoskeleton

a large network of proteins fibres with several roles

which two types of protein make up the cytoskeleton

actin filaments and microtubules

what are actin filaments

-small strands 7nm in diameter support the cell and give it mechanical strength,

-large strands 10nm in diameter anchor the nucleus and can extend between cells for communication

what are microtubules

-stacks of protein 18-30nm in diameter made from tubulin proteins

-assist microfilaments in giving the cell shape and support

-form the cilia, undulipodia and centrioles

-contain motor proteins that use ATP to move the cell's contents along the fibres

what is the function of the cytoskeleton

-helps a cell keep its shape

-moves chromosomes during cell division

-moves organelles around the cell

-extends into cilia and flagella to help cell movement (structure, transport and movement)

what is the function of flagella

-allow cells to move around

what is the function of cilia

move substances along the cell's surface

are eukaryotic or prokaryotic cells larger

eukaryotic:10-100um > prokaryotic:<2um

how is the DNA in eukaryotic and prokaryotic cells different

eukaryotic: linear , prokaryotic: circular

where is DNA found in eukaryotic and prokaryotic cells

eukaryotic: nucleus , prokaryotic: cytoplasm

what are cell walls made from in eukaryotic and prokaryotic cells

-eukaryotic: cellulose in plants/chitin in fungi , -prokaryotic: polysaccharides

which type of cell has membrane bound organelles

eukaryotic cells only

what are flagella (when present) made from in eukaryotic and prokaryotic cells

-eukaryotic: microtubules in 9+2 formation

-prokaryotic: protein flagellin arranged in a helix

how does the size of ribosomes vary between eukaryotic and prokaryotic cells

-eukaryotic: >20nm (80S) -prokaryotic: <20nm (70S)

which organelles are found in prokaryotic cells but not eukaryotic cells

Plasmids: loops of DNA

Capsule surrounding the cell wall: gives protection from the immune system

Flagella: locomotion

how do eukaryotic cells divide

mitosis and meiosis

how do prokaryotic cells divide

binary fission

how do eukaryotic cells reproduce

sexually and asexually

how do prokaryotic cells reproduce

asexually

how do organelles work together to produce and secrete a protein

-mRNA copies gene and leaves nucleus through pores

-mRNA attaches to ribosome which synthesises a protein

-protein is packaged into vesicles and transported to golgi,

-vesicle fuses with golgi and is packaged and modified,

-then collected in a vesicle and transported to the cell surface membrane

-fuses with it and the substance leaves the cell

what are the functions of water

-reactant

-solvent

-habitat

-used to transport substances

-used to control temperature

what is the structure of water

-polar molecule with covalent bonds between the hydrogen and oxygen atoms

-hydrogen bonds between molecules

why is water a polar molecule

-because it is covalently bonded

-delta (partial charges) accumulate: a δ- charge on the oxygen and δ+ charges on the hydrogens

why do hydrogen bonds form between water molecules

-the partial delta charges attract

-oxygen of one water molecule is attracted to a hydrogen from another molecule to form a hydrogen bond

-ndividually weak but collectively strong

what are the properties of water

-cohesion

-adhesion

-high specific heat

-high heat of vaporization

-less dense as a solid,

-good solvent

what are the advantages of water having a high specific heat capacity

-water doesn't experience rapid temperature changes which makes it a more stable habitat than on land

what are the advantages of water having a high latent heat of vaporisation

-water must absorb a lot of energy before it can evaporate

-helps organisms to cool down by processes such as sweating and transpiration

what are the advantages of water being less dense as a solid

-ice floats to the top of the body of water

-acting as a insulator

-habitat for some species

what are the advantages of water being cohesive

-water molecules are attracted to each other by hydrogen bonds

-so water can flow and be transported e.g. up plant stems

what are the advantages of water being a good solvent

-water is a good solvent because the δ+ hydrogens are attracted to negative ions

-δ- oxygens are attracted to positive ions

-ions can dissolve in water and be transported

define adhesion

attraction between molecules of different substances

define cohesion

attraction between molecules of the same substance

define latent heat of vaporisation

the amount of (heat) energy required to change the state of a substance from liquid to gas

define specific heat capacity

it is the amount of energy needed to raise the temperature of 1kg of a substance by 1°C

what are macromolecules

large complex molecules e.g. proteins

what are polymers

large, complex molecules composed of long chains of monomers joined together

what are monomers

small, basic molecular units

how are polymers made

-form chemical bonds between monomers and also produces water

how are polymers broken down

-break chemical bonds between monomers using water

which are the only elements found in carbohydrates

carbon (C), hydrogen (H) oxygen (O)

What is the ration of carbon to hydrogen to oxygen in carbohydrates

1:2:1 (CH2O)n

what are the bonds in carbohydrates called

glycosidic bonds

what are the monomers in carbohydrates called

monosaccharides

give three examples of monosaccharides

fructose, galactose, glucose

are monosaccharides soluble in water

yes

give three examples of disaccharides

lactose, maltose, sucrose

are disaccharides soluble in water

yes

give three examples of polysaccharides

cellulose, glycogen, starch

are polysaccharides soluble in water

no

what are the functions of carbohydrates

source of energy, used as storage, make up 10% of organic matter in the body

how are monosaccharides classified by their number of carbon atoms

triose (3 carbons), pentose (5 carbons), hexose (6 carbons)

what type of monosaccharide is glucose

hexose (6 carbons)

what are the two structural isomers of glucose

alpha (α) and beta (β) have the same chemical formula but a different structural formula

what is the difference between alpha and beta glucose

-alpha glucose the right hydroxyl group (OH) is below the plane

-beta glucose the right hydroxyl group (OH) is above the plane

what is the function of glucose

main energy source in animals and plants

what type of monosaccharide is ribose

pentose (5 carbons)

how is the structure of ribose different to glucose

5 carbons instead of 6, so one less C+H+OH

what is the function of ribose

the sugar component of RNA nucleotides