2b: Cell structure

nucleus

contains genetic material enclosed in a nuclear membrane

cytoplasm

liquid substance in which chemical reactions occur, contains enzymes and organelles

cell membrane

controls what enters and exits the cell

mitochondria

where aerobic respiration occurs, proving energy for the cells

ribosomes

site of protein synthesis within the rough endoplasmic reticulum

chloroplasts

site of photosynthesis containing chlorophyll

permanent vacuole

contains cell sap, found within cytoplasm and improves cell rigidity

cell wall

a wall of cellulose that provides strength to the cell

which of these is found ONLY in animal cells?

nucleus, cytoplasm, cell membrane, mitochondria, ribosomes

which of these is found ONLY in plant cells?

chloroplasts, permanent vacuole, cell wall

specialised cells

cells that have developed certain characteristics to carry out particular functions

how do cells specialise?

they undergo differentiation

differentiation

process involving the cell gaining new sub-cellular structures for it to be suited to its role

differentiation in animals

mostly only once

differentiation in plants

most cells can retain this ability

specialised cells in animals

- sperm cells
- nerve cells
- muscle cells

sperm cells

function: carry male's DNA to the egg cell for reproduction
- streamlined head and long tail for swimming
- many mitochondria to supply energy to move
- acrosome with digestive enzymes to break down outer layers of egg cell

nerve cells

function: transmit signals from one place to another in the body

muscle cells

function: specialise to contract and expand quickly

specialised cells in plants

- root hair cells
- xylem cells
- phloem cells

root hair cells

function: take up water by osmosis and mineral ions by active transport
- large surface area for more absorption
- permanent vacuole to speed up movement
- mitochondria for energy for active transport

xylem cells

function: transports water and mineral ions from roots to shoots

phloem cells

function: carries products of photosynthesis to all parts of the plant

stem cell

undifferentiated cell that can undergo division to produce many similar cells

types of stem cells

- embryonic
- adult stem cells
- meristems (plants)

embryonic stem cells

- form when egg and sperm fuse to form zygote
- can differentiate into any type of cell
- can be cloned
- could replace insulin-producing cells

adult stem cells

if found in bone marrow can form many types of cells

meristems

- found in root and shoot tips
- can differentiate into any type of plant
- can differentiate throughout plant life
- can be used to make plant clones

benefits of stem cells in medicine

- replace damage cells
- bone marrow transplants (treat blood cell cancers)
- can grow organs for transplant
- no rejection (if made from patient)
- allows testing without animals

risks of stem cells in medicine

- ethical issues (unused embryos)
- no guarantee of success
- possible long term effects
- mutations
- difficult to find donors