cell biology

Eukaryotic cells - complex, in animal and plant cells

Eukaryotes - organisms made of eukaryotic cells

Prokaryotic cells -  small, simple, (bacteria)

Prokaryotes - single-celled organism, one prokaryotic cell

Both - contain subcellular structure

Nucleus - controls genetic material, controls activities of the cell

Cytoplasm - gel-like substance, chemical reactions happen, contains enzymes that control reactions

Cell membrane - holds cell together, controls what goes in and out

Mitochondria - aerobic respiration reactions take place here, respiration transfers energy that cell needs to work

Ribosomes - where proteins are made

Cell wall - rigid cellulose structure, supports and strengthens cell

Permanent vacuole - contains cell sap, weak solution of sugar and salts

Chloroplasts - photosynthesis occurs, makes food for plant, contain chlorophyll

Chlorophyll - absorbs light needed for photosynthesis

• are prokaryotes
• has cytoplasm, cell membrane and cell wall
• doesn't have a nucleus
• has a singe, circular strand of DNA floating freely
• contains plasmid

Plasmid - small rings of DNA

Light microscope 

• uses light and lenses
• helps us see individual cells and large subcellular structures

Electron microscope

• use electrons instead of light
• higher magnification and resolution 
• helps us see smaller things in more detail (ribosomes, chloroplasts, plasmids)

1. prepare the slide

2. clip slide onto the stage

3. select the lowest-powered objective lens

4. use the adjustment knob to move the stage up tp just below the objective lens

5. look down the eyepiece

6. adjust focus on fine adjustment knob until a clear image is given

• magnification = image size ÷ real size
• 2 ÷ 0.02 = 100  magnification = x 100

• image size = magnification × real size
• 50 × 0.3 = 15  image size = 15 mm

• real size = image size ÷ magnification
• 100 ÷ 400 = 0.025  real size = 0.025 mm

• performs specific functions
• most cells in organisms are specialised cells
• specialised cells look different to normal cells

Differentiation - the process by which cell changes to become specialised for a job

• cells develop different subcellular structures as they specialise
• differentiation occurs as an organism develops
• stem cells are undiffrentiated cells

• only in animal cells
• used for reproduction
• the function is to get male DNA to female DNA
• long tail, streamlined head to help swim to the female egg
• lots of mitochondria to provide energy
• carries enzymes to digest through the egg cell membrane

• only in animals
• used for rapid signaling
• the function is to carry electrical signals from one part of the body to another
• long, branched connections at either end

• only in animals
• used for contraction
• the function is to contract quickly
• long, lots of mitochondria to transfer energy needed 

• only in plants
• on the surface of plant roots
• used for absorbing water and minerals
• grow into "long hairs" that stick out into the soil
• gives the plant a big surface area for absorbing water and minerals

• only in plants
• used for transporting substances
• form phloem and xylem tubes
• transport food and water around plants
• cells are long and joined end to end

Xylem tubes - hollow in the centre

Phloem tubes - very few subcellular structures so substances can flow through

• contains genetic material (chromosomes)
• body cells have 2 copies of each chromosome
• 1 from "mother" and 1 from "father"
• 23 pairs of chromosomes

• chromosomes are long lengths of DNA
• DNA is coiled up to form chromosomes
• each chromosome carries a large number of genes
• genes are short sections of DNA
• genes control characteristics

Mitosis - when a cell reproduces itself by splitting to form two identical offspring

• use mitosis to grow and develop or replace damaged cells

Growth and Replication

• DNA is spread out in long strings
• cell grows and increases amount of mitochondria and ribosomes
• duplicates its DNA

Mitosis

• chromosomes line up in cell and fibres pull them apart
• two arms of chromosomes go to opposite ends of cell
• membranes form around chromosomes
• nucleus, cytoplasm and cell membrane divides

• undifferentiated cells
• divide to produce lots of undifferentiated cells
• develop into different types of cell
• found in early human embryos
• adults have stem cells in their bone marrow
• adult stem cells can only turn into blood cells
• stem cells can be grown in a lab to produce clones

• used to cure disease
• stem cells turn into blood cells to replace faulty ones

Bone marrow - tissue found inside the bone

For example - people with blood disease can be treated by bone marrow transplants

• used to replace faulty cells in sick people in the future
• considered unethical by some people

Therapeutic cloning - embryo can be made to have the same genetic information as a patient, which means they wouldn't be rejected

Risks - stem cells could've been contaminated with a virus which could be passed onto patients making them sicker

Embryonic stem cells

•  each one is a human life (unethical)
• embryos are unwanted by fertility clinics
• researchers should alternative sources
• uses of embryonic stem cells banned in some countries but not in UK

• found in meristems
• cells can differentiate into any type of plant cell
• used to produce clones of whole plants quickly and cheaply
• useful for growing crops with desired features
• useful for growing plants of rare species

Diffusion - spreading out of particles from an area of high concentration to an area of low concentration

• happens in both solutions and gases

For example - after spraying perfume in a room, the smell diffuses through the air in the room

• dissolved substances can move in and out of cells by diffusion
• only small molecules (oxygen) can diffuse through a cell membrane
• large molecules (starch, proteins) can't fit through the membrane

For example - the concentration of particles is higher inside the cell than outside, so net movement of particles is out of the cell

• can vary

Concentration gradient

• bigger concentration gradient, faster rate of diffusion
• because net movement from one side is greater

Temperature

• higher temperature, faster rate of diffusion
• because particles have mroe enrgy so move around faster

Surface area

• larger surface area, faster rate of diffusion
• because more particles can pass through at once

Osmosis - the movement of water molecules across a partially permeable membrane from an area of higher concentration to an area of lower concentration

Partially permeable membrane - very small holes in it, only tiny molecules (water) can pass through and big molecules (sugar) can't

• osmosis is a type of diffusion

• water moves either into the cell from the surrounding solution or out of the cell by osmosis

Short of water

• solution inside is quite concentrated 
• solution outside is dilute
• water moves into cells by osmosis

Lots of water

• solution inside is dilute
• water is drawn out of the cell and into fluid outside through osmosis

Active transport - the movement of particles against a concentration gradient using energy transferred during respiration

• used to move substances in and out of cells
• allows cells to absorb ions from very dilute solutions

• plants need mineral ions for growth
• root hair cells cant use diffusion to take minerals from the soil
• active transport allows plants to absorb minerals from dilute solution against a concentration gradient

• used in the digestive system
• lower concentration of nutrients in the gut, a higher concentration of nutrients in the blood
• active transport allows nutrients to be taken into the blood
• essential to stop us starving
• glucose can be transported to cells used for respiration

• lungs transfer oxygen to blood to remove waste carbon dioxide
• gas exchange takes place at alveoli
• alveoli surrounded by capillaries
• oxygen diffuses out of the air in the alveoli into blood in capillaries

Maximizes diffusion of oxygen and carbon dioxide

• enormous surface area
• moist lining for dissolving gases
• very thin walls
• good blood supply

• nutrients (glucose, amino acids) absorbed into the bloodstream from the small intestine
• small intestine covered in millions of tiny projections (villi)

Villi - a single layer of surface cells, the very good blood supply to assist quick absorption

• plants need carbon dioxide for photosynthesis
• carbon dioxide diffuses into air spaces within leaf
• then diffuses into cell where photosynthesis happens

Exchange surface

• covered in stomata which carbon dioxide diffuses through
• oxygen and water vapor also diffuse out of stomata

Flattened shape

• increases area of exchange surface
• so more effective

Walls of the cell

• air spaces inside leaf increase area of exchange surface
• more chance for carbon dioxide to get into cells

Stomata

• plant losing water, guard cells close stomata
• decreases the chance of plants to wilt (droop)

• water enters through the mouth
• passes out the gills
• oxygen diffuses from water into blood in gills
• carbon dioxide diffuses from blood into water

Gill filaments (thin plates)

• give a large surface area for the exchange of gases
• increases the rate of diffusion

Lamellae

• increases surface area
• lots of blood capillaries speed up diffusion between water and blood
• thin surface layer to minimize distance gases have to diffuse