Biology - Unit 1-9

Light microscope

use a beam of light to form an image

Electron microscope

use a beam of electrons to form an image

Features of the light microscope [4]:

• magnify up to 2000x

• relatively cheap

• portable

• can magnify live specimens

Features of the electron microscope [4]:

• magnify up to 2000000x

• very expensive

• immovable

• need special temperature, pressure and humidity

What electron microscope creates high quality 2D images?

Transmission electron microscope

What electron microscope creates low quality 3D images?

Scanning electron microscope

Image size =

Magnification x Real size

Resolving power

the capacity of a microscope to distinguish between two separate points

Organelles in an animal cell [5]:

• nucleus

• cytoplasm

• cell membrane

• mitochondria

• ribosome

Nucleus

controls activities in the cell and contains genetic information

Cytoplasm

organelles are suspended and chemical reactions take place

Cell membrane

controls the movement of substances in and out of the cell

Mitochondria

where aerobic respiration takes place

Ribosome

where protein synthesis takes place

What organelles are unique to plants and algae? [3]

• cell wall

• chloroplast

• permanent vacuole

Cell wall

a cellulose casing which strengthens and supports the cell

Chloroplast

organelles containing chlorophyll to absorb sunlight for photosynthesis

Permanent vacuole

space in cytoplasm filled with cell sap - keeps cells rigid

Eukaryotic cell

cell with a nucleus

What organisms are eukaryotes? [4]

• animals

• plants

• fungi

• protista

Prokaryotic cell

cell without a nucleus

What do bacteria have instead of a nucleus?

a ring of genetic material and individual plasmids

Plasmid

extra small rings of DNA for very specific features

Adaptations of the neurone [3]:

• many dendrites to connect to other cells

• long axon to carry the nerve impulse

• myelin sheath to insulate

Adaptations of striated muscle cells [3]:

• special proteins that slide over each other

• many mitochondria to transfer energy for contraction

• store glycogen, insoluble chain of carbohydrates

Adaptations of sperm cells [4]:

• flagella for moving withing the female reproductive system

• many mitochondria to transfer energy for the flagella

• acrosome stores digestive enzymes to break down the egg

• large nucleus for genetic information

Adaptations of root hair cells [3]:

• increased surface area for osmosis

• large permanent vacuole to speed up osmosis

• many mitochondria to transfer energy for active transport

Adaptations of photosynthetic cells [3]:

• contain chloroplasts containing chlorophyll to absord energy

• positioned in continuous layers in leaves and stem to absorb energy

• large permanent vacuole to keep cell rigid for stem and leaf support

Adaptations of xylem cells [2]:

• build up lignin spirals then die to form long, hollow tubes

• spirals and rings of lignin make cells strong to withstand pressure of water moving up the plant

Adaptations of phloem cells [2]:

• cell walls between cells break down into sieve plates

• lose internal structures but are supported by companion cells

What does the xylem carry?

water and mineral ions

What does the phloem carry?

nutrients from photosynthesis

Diffusion

the spreading out of particles in a fluid

What is the net movement in diffusion?

from an area of high concentration to an area of low concentration

What increases the rate of diffusion? [2]

• a large concentration gradient

• higher temperature

net movement =

particles in - particles out

How do cells speed up diffusion?

higher surface area (microvilli, protrusions)

Osmosis

water moves across a partially permeable membrane from an area of high concentration to an area of low concentration

Partially permeable membrane

a membrane that only lets some types of particles through

Isotonic

concentrations are the same in and out

Hypertonic

water concentration is higher in than out

Hypotonic

water concentration is higher out than in

What happens to an animal cell in a hypertonic solution?

it becomes shrivelled

What happens to an animal cell in a hypotonic solution

it may burst

Turgor

water pressure in a plant cell

What condition must plant cells be kept in?

hypotonic solutions (keep turgid)

What happens to a plant cell in a hypertonic solution?

plasmolysed

What happens to a plant cell in a hypotonic solution?

turgid

What happens to a plant cell in an isotonic solution?

flaccid

What happens to plants if their cells are not turgid?

They wilt

How to investigate osmosis:

Put chips of plant tissue into solutions with different concentrations of salt or sugar, then find the difference in mass from start to finish.

Active transport

the movement of substances across a partially permeable membrane, against the concentration gradient

What is needed for active trasport?

mitochondria, which respire, which releases energy

Active transport in plants:

the root hair cells take nitrate and other ions out of dilute solutions in the soil

Active transport in animals:

glucose sometimes must be actively transported from the gut to the blood

Surface area to volume ration (SA:V)

the ratio of an organism’s surface area to its volume

What SA:V ratio is ideal for diffusion and why?

a small one, as it gives short diffusion distances

How does a large SA:V affect diffusion?

simple diffusion is no longer enough for the organism, as the distance from the centre and the surface increases

Downsides of a large SA:V [2]:

• gas and food molecules cannot reach every cell

• metabolic waste cannot be removed fast enough

Adaptations for exchanging materials [4]:

• large surface area for exchange

• thin membrane for a short diffusion path

• efficient blood supply to maintain a steep concentration gradient

• being ventilated to maintain a steep concentration gradient

How are the lungs adapted for gas exchange? [4]

• ventilated

• large surface area

• rich blood supply

• short diffusion path

How are gills adapted for material exchange? [4]

• ventilated by operculum

• large surface area from filaments

• rich blood supply

• short diffusion path

How are plant roots adapted for material exchange? [2]

• large surface area

• transpiration stream moves water away, keeping steep concentration gradient

How are plant leaves adapted for material exchange? [2]

• large surface area (thin,flat leaves; air spaces in leaf tissues, stomata)

• steep concentration gradient maintained

Cell division

the formation of two genetically identical daughter cells

Where are the chromosomes?

in the nucleus

What are chromosomes?

long, thin strings of genes that contain instructions for making new cells

What are genes?

Genes are sections of DNA that control a single genetic trait.

How many chromosomes are in the nucleus of a body cell?

46 chromosomes

How are chromosomes arranged in cells?

23 pairs - one from mother and one from father

How many chromosomes do gametes have?

23 chromosomes

Cell cycle

series of events that cells go through as they grow and divide

Mitosis

asexual reproduction by splitting the nucleus

How long is the cell cycle?

24 hours to several years

When is the cell cycle rapid?

as a baby develops and throughout childhood

When does the cell cycle slow?

after puberty

What areas continue rapid cell division in adults? [4]

the hair follicles, the skin, the blood, the lining of the digestive system

Cell cycle: stage 1 [4]

• longest stage

• cells grow bigger and increase mass

• replicate DNA to form two copies of each chromosome

• replicate organelles

Cell cycle: stage 2 [3]

• mitosis

• one set of chromosomes is pulled to each side

• nucleus divides

Cell cycle: stage 3 [1]

• cytoplasm and cell membranes divide to form daughter cells

Diploid

46 chromosomes

Interphase [3]

• cell grows

• cell replicates chromosomes

• organelles replicated

Prophase [3]

• chromosomes condense

• nuclear membrane dissolves

• spindle fibres form

Metaphase [2]

• nucleus dissolves

• chromosomes align in centre

Anaphase [1]

• chromosomes moved to opposite poles of cell

Telophase [3]

• just before cells split

• nuclear membranes reform

• spindle fibres dissolve

Cell cycle order

• interphase

• prophase

• metaphase

• anaphase

• telophase

Differentiation

process in which cells become specialised in structure and function

Stem cells

cells that can differentiate into specialised cells

Embryonic stem cells

can differentiate into any kind of cell

Adult stem cells

can only differentiate to a limited set of cells

What organism can differentiate all through life?

plants

Where are undifferentiated cells found in plants?

meristem (stem and roots)

What is special about plant cells?

they can redifferentiate

Cloning in plants

You take cuttings from good parent plants and then planting them in moist conditions to produce clones of the parent plant.

Zygote

fertilized egg

Where are embryonic stem cells found?

inner cells of early embryo

Where can adult stem cells be found?

bone marrow

When might adult stem cells be used?

after injury

How could we use stem cells in medicine? [6]

• body parts for transplant

• replacing nerves (paralysis)

• curing blindness

• treat type 1 diabetes

• treat infertility

• treat dementia