GCSE biology // Topic 1 // Cell biology

cell defenition

basic unit of all forms of life

prokayotic and eukaryotic cell defenition

eukaryotic cells contain their genetic material enclosed (in a nucleus) whereas prokaryotic cells don not contain their genetic material in a nucleus - it is frede in the cytoplasm as a single loop of DNA and plasmids

what cells are pro and eu karyotic ?

All fungal animal and plant cells and protoctists are eukaryotic

all bacterial cells are prokaryotic

eukaryotes can either be -uni or -multi cellular

but all prokaryotes are unicellular

and all -multi are eukaryotes

things that eukaryotic cells have fundamentally

Plant and animal cells (eukaryotic cells) have a cell membrane,

cytoplasm and genetic material enclosed in a nucleus.

have membrane bound organelles e.g. nucleus (mitochondria)

cellulose cell walls

things that prokaryotic cells have fundamentally

cytoplasm and a cell membrane surrounded by a cell wall. The

genetic material is not enclosed in a nucleus. It is a single DNA loop and there may be one or more small rings of DNA called plasmids - none have mitochondria nucleus or chloroplasts

maybe have ribosomes

not cellulose cell walls

much smaller than EUK cells in comparison

cell replication difference between prokaryotic cells and eukaryotic cells

since all prokaryotes (bacteria) (or unicellular eukaryotes) are unicellar when they divide they create whole new organisms therefore it is asexual reproduction

unicellular eukaryotes are only growing or replacing cells when they divide, they arent making new organisms

5 organelles common to animal and plant cells and 3 extra that only plants have

common : Cytoplasm, cell membrane, mitochondria, ribosomes, nucleus

plant : permanent vacuole, chloroplast, cell wall

nucleus

contain the genetic material that controls the activities of the cell

cell membrane

encolses the cell controls the movement of substances into and out of the cell

cytoplasm

gel-like solution where chemical reactions take place. contains enzymes to control these reactions

mitochondria

site of the most chemical reactions for aerobic respiration , to release energy for the cell (contains enzymes to)

ribosomes

sites of protein synthesis (proteins arereally important e.g. enzymes)

chloroplasts

sites of photosynthesis by absorbing light and producing glucose from CO₂ and H₂O (contains enzymes to)

cell wall

made of cellulose which strengthens the cell and gives structure + support to it, stops it from bursting 

permanent vacuole

filled with cell cap (weak solution of salts and sugars) which help gives the plant cell its shape, keeps it turgid (swollen)

how sperm cell is adapted to its function

function - to combine its genetic material with an egg cell

long tail and streamlined head to help it swim to the egg

have lots of mitochondria providing the energy needed for swimming

carries enzymes in its head which allow them to digest through the egg cell membrane

how nerve cells are adapted to its function

function : to send electrical impulses around the body

long axon (which carries the impulse), so that nerves can run to and from different parts of the body to the central nervous system.

extensions and branches, so that it can communicate with other nerve cells, muscles and glands.

axon insulated by myelin sheath, which insulates the nerve cell and speeds up the nerve impulse.

how muscle cell is adapted to its function

function : to contract (get shorter)

Muscle cells contain filaments of protein that slide over each other and change their length (shorten) to cause muscle contraction.

When the cell contracts the filaments silde over each other and shorten - contracting

contain many mitochondria to provide energy needed for muscle contraction

they work together to form tissue

how root hair cell is adapted for its function

function : to absorb water and dissolved mineral ions from the soil

The root hair cell increase the surface are of the root to provide contact with soil water.

It has thin walls so as not to restrict the movement of water and create a short diffusion path

do not contain chloroplsts as they are underground and. dont recieve light

how xylem cell is adapted for its function

function : form long tubes in the plant stem to carry water and dissolved minerals from the roots to the leaves

very thick walls containing lignin which provides support to the plant

the end walls between the cells have broken down - so the cells now form a long hollow tube so water and dissolved mineral ions can flow easily

no internal sub cellular structures (e.g. mito. c.plasm ) makes it easier for water and dissolved mineral ions to flow

how phloem cell is adapted for its function

function : work as tubes and carry dissolved sugars up and down the plant

phloem vessel cells have no nuclei and limited cytoplasm and have pores called sieve plates at the end of the vessel cells - both features allow dissolved sugars to move through the cell interior

because of limited c. plasm in vessel cells they dont have many m.chondria each vessel cell has a companion cell connected by pores - m.chondria in the companion cell provide energy to the phloem vessel cell

why cell differentiation is important

important because it allows production of different tissues and organs that perform various vital functions in the organism. As an organism develops, cells differentiate to form different types of cells.

cell differentiation to become specialised

what differentiation is

what happens as a cell differentiates

Most cells are specialised and are adapted for their function. they have adaptaions which help them carry out their particular function.

Differentiation is the process by which a cell becomes specialised

As a cell differentiates it acquires different sub-cellular

structures to enable it to carry out a certain function. It has become a specialised cell

animal and plant cell cell differentiation points

• Most types of animal cell differentiate at an early stage.

• Many types of plant cells retain the ability to differentiate throughout life.

In mature animals, cell division is mainly restricted to repair and

replacement.

how to ready a slide for m.scope focusing viewing

place the slide on the stage and use the clips to secure the slide in place, then select the lowest power obj. lens

then need to position the obj lens so that it almost touches the slide - using the coarse focusing dial. , when it almost touches the slide we stop

why we turn dial for readying whilst looking at the m.scopes side instead of through

important that we look at the side of the m.scp not through as greater risk of obj lens and slide crashing and being damaged that way

focusing the m.scp

then turn coarse focusing dial whilst looking through the eyepiece to inc. dist. between stage and slide, do this until the cells come into a rough focus,

then use the fine focusing dial to bring the cells into a clarified focus

then you can select a higher power obj. lns , and only use the fine focus then

preparing onion epidermal tissue to be viewed under an m.scp

firstly cut the onion and peel a thin layer of tissue using tweezers, - so that light can penetrate the layer so the sub-cellular structures and cells can be viewed w clarity

then use iodine solution to stain the cell to add contrast and help see part of the cells w more clarity - (leave some time so the iodine can react)

Cover slip is lowered at an angle + gently to stop air bubbles getting in an obstructing specimen view

(so will fingerprints so hold cover slip and slide by its slides)

(water+)

associated risks w slide preparation and

sharp knife cutting the onion - risk of cutting yourself - cutting on a board, carefully and conciously (fingers away)

iodine sol. - contact w eyes, skin [ harmful - wear safety goggles + gloves

cover slip small glass pieces shattering - getting into the body - hold slide carefully, and look at mscp from side when bringing slide as close to lens as possible when focusing

drawing rules

title underlined

makes space of drawing provided

pencil

single clear lines - no sketchy, no gaps, no shading

pencil ruler labelled lines - no arrowheads - shouldn’t cross - horizontal

include mgn + scale bar

magnification

resolution

number of times larger the magnified image is compared to the real size of the specimen

the ability to distinguish between two points rather than merged into one (until a certain closeness of the points)

total mgn + mgn formula

total mgn = eyepiece lens * obj lens

mgn = image size / acc size (constant units)

remember using mia / m=i/a

light m.scope limits of mgn and res (resolving power) + ppl

robert hooke first to observe cells - then upto improved of 270X - it was progressing - using series of lenses and light

allows up to 2KX and 200nm res

however res is limited, even if we were to keep magnifying - less clarity

m.scopy - what the spec has to say

An electron microscope has much higher magnification and resolving power than a light microscope.

This means that it can be used to study cells in much finer detail.

This has enabled biologists to see and understand many more sub-cellular structures.

e- m.scop

beam of electrons rather than light, so vaccum is needed, electromagnets are used for focusing instead of lenses

up to 2 mil X mgn and 0.2 nm res

much greater mgn and res than l. mcps

black and white but computerised colour often added

comparisons of one another e- scopes w light scopes

e- is much bigger, more expensive, requires training to use, specimen must be dead, black and white

differentiation

As an organism develops, (stem) cells differentiate to form different types of cells - to carry out specific functions in the body

• Most types of animal cell differentiate at an early stage.

• Many types of plant cells retain the ability to differentiate throughout life

in adult animals, diff. is limited to replacement and repair

what happens during differentiation

As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell

chromosomes and gametes

EUKs have chromosomes in nucleus and they are made of DNA molecules. Body cells contain two of each chromosome. Human cells contain 23 pairs of chromosomes (for the eg. cell there are 2 pairs of c.somes - 4 )

however gametes - sperm, egg only contain half the chromosomes (genetic material) as they fuse together

the pairs are genetically identical - homologous , and are matched based on size and shape

genes and multicellular need

each chromosome carries a large number of genes (coding for a specific protein) , and these determine many of our features

DNA carry the code that controls cellular functions and activities

animals and plants are multicellular so have lots of cells so they must be able to divide - Cells divide in a series of stages called the cell cycle

cell stuff b4. mitosis

Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome.

They are also checked so that they are correct

chromosomes explanation of the e.g. cell when being copied

The copies stay attatched

(for the e.g cell, that is still two pairs of chromosomes in an x shape - but one end of the x shape is a chromatid that will eventually break off into its own chromosome - so as of now it as 2 copies of 2 pairs that have two potential chromosomes (chromatids) - 8P as 2×2×2

mitosis (stage 2) :

In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus (membrane) divides.

Final stage of the CC the cytoplasm and cell membranes divide to form two genetically identical cells.

functions and importance of mitosis

essential for growth and development of multicellular organisms (plants and animals)

takes place when an organism repairs or replaces damaged or worn-out cells

happens during asexual reproduction

cell cycle time phase length formula + explanation

= observes no. of cells at that stage / total no. of cells observed (physically there at whatever stage) * (length in time of one cycle)

this method takes into account the proportion of cells in a stage out of the total number of cells relative to the time it takes for one division

(less cells there are the faster it takes)

humans progression from fertilisation + embryonic S cells.

humans start as a zygote (fertilised egg cell). the zygote undergoes mitosis to form a ball of cells called the embryo. they furtherly divide to get more, and diff. into specialised cells e.g. muscle and nerve → which then forms the final organism

cells in the early embro have not differentiated. Any cells is capable of diff. into any type of body cell - are called embryonic stem cells.

SC defenition

A stem cell is an undifferentiated cell which can give rise to more cells of the same type and can diff to form other types of cells

embryonic (early age) vs. adult SCs

(embryonic can diff into any - however SCs of the organ and only diff into related cells (few types of cells) e.g. Bone M → RBCs, WBCs + platelets) - adult stem cells cannot diff. into any other type of cell

|→ This is why most animals diff. at an early age , and why diff in adults is js limited to repair and replacement of cells

some specialised cells cannot be re diff.ed into

bone marrow transplant

Leukaemia is a cancer of the bone marrow

To treat this, the patients first existing bone marrow is destroyed using radiation

The patient then recieves a transplant of the bone marrow from a donor

the SCs in the bone marrow now divide and form new bone marrow. They also diff. and form blood cells

problems w bone marrow transplant

donor has to be genetically compatible with the patient or else the WBC produced by the donated BM could attack the patients body. → immunosuppressant drugs that could make it easier to contract infection

Risk of viruses being passed down from donor to patient

therapeutic cloning

In therapeutic cloning, an embryo is produced with the same genes as the patient.

Stem cells from the embryo can be transplanted into the patient (stimulated for division) without being rejected by the patient's immune system.

Once inside the patient, the stem cells can then differentiate to replace cells which have stopped working correctly.

(can be used to treat lots of medical conditions like diabetes or paralysis - some ppl have ethical or religious objections to the procedure)

plant stem cells

shoots and toots tips and buds contain meristem tissue. These stem cells can differentiate into any type of plant tissue, at any point in the life of the plant.

Stem cells from meristems in plants can be used to produce genetically identical clones of plants quickly and economically.

• Rare species can be cloned to protect from extinction.

• Crop plants with special features such as disease resistance / appearance / taste / or certain nutrients can be cloned to produce large numbers of identical plants for farmers.

diffusion definition

(the spreading out of particles resulting in a) net movement from an area of higher concentration to and area of lower concentration (down the concentration gradient)

passive process - no Ê required

example of O2 and CO2 diff. into and out of cells

cells need O2 to release Ê through aerobic resp by mitochondria

cells are surrrounded by a high concentration of oxygen (from the blood - from the lungs)

higher conc. out → lower conc. in (by diff.)

now CO2 is produced and there is a higher conc of it inside the cell than outside, so CO2 diff. out

urea : inside cells to outside

main - factors affecting the rate of diff.

conc. grad. : the greater difference between concentration the more molecules can diffuse in a given time (due to the difference) therefore an increased rate in diff.

higher temp : greater rate of diff. because particles have more Kin Ê and therefore are moving faster

SA of the membrane - a greater SA membrane means that molecules can diffuse at a greater rate due to the bigger space

periphery factors affecting the rate of diff.

path - shorter diff. path means that molecules can travel faster and a greater rate of diff.

membrane structure - the permeability - larger pores = faster

type of molecule - smaller molecules = faster more soluble in the barrier therefore faster (lower relative molecular mass means that they are also lighter)

SA : V in unicellular organisms

unicellular organisms have a very high SA : V , meaning that for their volume they have a really large SA

this means that they can rely on diff to transport molecules into and out of the cell e.g. all the O2 and CO2

trend of SA : V as organisms get larger

and how mult. animals have adapted to this problem

as organisms get larger their SA:V falls sharply - big problem for multicellular organisms - their SA is not large enough for their volume for diffusion of particles

cells on the surface can get enough O2 by diff however not enough O2 can diffuse into the cells into the center of the organism as it is too far away from the surface (length from Surface to center inc.)

they have specialised exchange structures for gas exchange w a v. high SA

they have a transport system to carry gases around the body

how gills bring O2 into the fish

O2 aq water passes into the mouth, where it then flows over the gills, where the O2 is transported into the bloodstream

deo2 bl passes into the fillament where O2 diffuses from the water into the blood. O2 bl returns into the fish

gills adaptations for an efficient exchange surfaces

gills are covered in very fine folded fillaments meaning that they have a really large SA (inc. rate of diff)

fillaments have a thin membrane so the diff path is short so greater rate

dense capillary network that rapidly takes away exchanged molecules ensuring that the conc. grad. is always high

SA:V experiment with agar cubes

agar cube has a similar consistency to cytoplasm and has lots of water, in the center there is a block of some random chemical that is purple and disappears when reacted w acid

there are 3 agar cubes w an equal sized cube of the chemical inside but different side lengths

we put cubes into the beaker and submerge w acid

record how long it takes for a colour change

explanation of the Agar jelly cube SA:V experiment

the larger the cube, the lower SA:V

meaning that the rate of diffusion in proportion of the length to the center of the cube (where the chemical is) decreases,

therefore it takes longer for the acid to diffuse through to reach the center

this is the same w organisms as the larger the organism the lower sa - molecules can only diffuse into the outer cells

Osmosis definition

Overall (net) movement of water from an area of higher water potential (dilute solution) to an area of lower WP (conc. sol.) [down the conc grad] through a partially permeable membrane

Osmosis explanation

partially permeable means that it is decisive on what it will let through e.g. water is small so it is permeable through thr membrane but not sugar - this means that only water can pass to neutralise solution conc.

water moves both ways but moves net from the area of high conc. to the area of low conc. down the CG

will occur when there is a conc. grad. between the WPs of the solutions. (always specify what is moving, from where and by what process)

osmosis in tissue fluid transmission

Body cells are surrounded by tissue fluid (glucose and other substances dissolved), formed from squeezed plasma out of capillaries

transport between molecules between cell. c.plasm and this fluid

it is important that the TF and c.plasm have the same WP so osmosis doesn’t occur and cells do not shrink or swell up and burst

and also so that only the substances needed e.g. O2 diffuse

possibilites of osmosis in animal cells

where the cell is placed in a solution w a lower WP, water moves out by osmosis net down the CG, causing it to shrink and be crenated

when placed in a solution w a higher WP, water moves in by osmosis net, causing it to swell ; it may burst as the CM may not withstand the force (lysis)

possibilites of osmosis in plant cells

where the cell is placed in a solution w a lower WP, water moves out by osmosis net down the CG, causing it to shrink and be plasmolysed - CW wont shrink

when placed in a solution w a higher WP, water moves in by osmosis net, causing it to swell (turgid) it does not burst as the membrane pushes onto the CW

osmosis potato experiment set up

take a corkscrew borer through a potato and cut the drill piece into 5 equal slices of length (no skin), and weigh the mass of each

place one slice in distilled water, and the other four in distilled concs. of sugar solution, and leave for a day

then pat dry v. gently the surface moisture and measure again

calc % change and plot the graph

factors to control in the osmosis experiment

temperature - affects rate of diff

skin and length (why we use a corkscrew borer) - controlling sa and v

vol of solution

time left in solution

same potato to ensure same WP inside the potato

explanation of the osmosis potato practical

the one w distilled water has a higher WP and the potato so water will move net in by osmosis (mass gain)

one w a more concentrated one than the potato has a lower WP and therefore water moves out net by osmosis (mass lost)

(the difference in WP between the potato and sol will determine how much mass is lost or gained as part osmosis water)

on the graph of mass change against conc. x int is the approx. conc. of the potato

eval. of the osm potato experiment

more data and in between concentrations makes the LOBF more accurate as more points / pattern more clear and accurate

reruns and mean for mass change makes the data more reliable

an error could be squeezing osmosis water out of the potato when drying or not enough surface moisture removed causing result innacuracies

Active transport

The movement of particles from an area of lower to higher concentration against the conc. grad. {caused by the cell} will take place in the cell by protein pumps and involes Ê from resp. (m.chon)

it is caused because the villi, roots, or kidneys need to take in as many molecules as possible

benefits and general adaptations of cells for AT

in RHCs, if more mineral aq+ are taken into the cell, this makes the WP of the cell c.plasm lower therefore causing osmosis to occur into the cell

lots of well developed m.chon to release energy for AT by resp

also have a thin, high SA membrane

Osmosis, AT, DIFF differences

Diff and Osm are passive processes, where AT is not

Diff and Osm happen down the CG where as AT draws against

Osm can only happen when the membrane is par perm in favour of water only (or else any other substance can move to equalise conc, not js water alone)

Osm is only water where Diff and AT are any