characteristics of living organisms
eukaryotic organisms
Eukaryotic organisms can be multicellular or single-celled and are made up of cells that contain a nucleus with a distinct membrane
plants
contain chloroplasts to carry out photosynthesis
have cellulose cell walls
store carbohydrates as starch or sucrose
animals
don't contain chloroplasts
don't have cell walls
can't photosynthesis
store carbohydrates as glycogen
have a nervous system
can move from place to place
cell structures
nucleus
contains genetic material in chromosomes which control how cells work
controls cell division
cytoplasm
supports cell structures
site of many metabolic reactions
contains water and many solutes
cell membrane
holds the cell together
controls the substances entering and leaving the cell
cell wall
supports the cell and defines its shape
chloroplasts
site of photosynthesis
the chlorophyll absorbs light energy needed for the reaction to occur
vacuole
contains cell sap
used for storage of certain material
also helps support the shape of the cell
mitochondria
site of aerobic respiration
ribosomes
site of protein production in protein synthesis
plant vs animal cells
plants have a cell wall made of cellulose, a permanent vacuole filled with cell sap and many plant cells also contain chloroplasts. none of these are found in animal cells
specialised cells
those which have developed certain characteristics in order to perform particular functions
cells specialise by undergoing differentiation
cells can either differentiate once early on or have the ability to differentiate their whole life (stem cells)
examples of specialised cells
sperm cells
specialised to carry the male's DNA to the egg cell for successful reproduction
streamlined head and long tail to aid swimming
many mitochondria to supply the energy to allow the cell to move
the tip of the head has digestive enzymes which break down the outer layers of membranes of the egg cell
nerve cells
specialised to transmit electrical signals quickly from one place in the body to another
the axon is long, enabling the impulses to be carried along long distances
having lots of extensions from the cell body (dendrites) means branched connections can form with other nerve cells
he problems arising from the disposal of radioactive waste and how the associated risks can be reduced
muscle cells
specialised to contract quickly to move bones
special proteins slide over each other, causing the muscle to contract
lots of mitochondria to provide energy from respiration for contraction
he problems arising from the disposal of radioactive waste and how the
associated risks can be reduced
root hair cells
specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
have a large surface area due to root hairs
the large permanent vacuole affects the speed of movement of water from the soil to the cell
mitochondria to provide energy for the active transport of mineral ions into the root hair cell
xylem cells
specialised to transport water and mineral ions up the plant
lignin causes the cells to die, becoming hollow and they are joined end to end to form a continuous tube so water and mineral ions can move through
phloem cells
specialised to carry the products of photosynthesis to all parts of the plants
cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells
stem cells
characteristics
a stem cell is an undifferentiated cell which can undergo division to produce many more similar cells
some of these will differentiate to have different functions
they are important in growth, development and repair
embryonic stem cells
form when an egg and sperm cell fuse to form a zygote
they can differentiate into any type of cell in the body
scientists can clone these cells and direct them to differentiate into almost any cell in the body
these could potentially be used to replace insulin-producing cells in those suffering from diabetes for examples
adult stem cells
if found in bone marrow, they can form many types of cells including blood cells
meristems in plants
found in root and shoot tips
they can differentiate into any type of plant, and have this ability throughout the life of the plant
they can be used to make clones of the plant
stem cells in medicine
benefits
risks
can be used to replace damaged cells, such as in type 1 diabetes, multiple sclerosis and paralysis caused by spinal cord injuries
bone marrow transplants for adult stem cells can be used to treat blood cell cancers, such as lukaemia
can grow whole organs for transplants
no rejection as it is made from the patients own cells
can allow for the testing of millions of potential drugs without animal testing
ethical issues of destroying unused embryos
no guarantee in how successful these therapies will be and if there will be any long term effects
mutations could occur in cultured stem cells
difficult to find suitable stem cell donors
levels of organisation
organeele, cell, tissue, organ, organ syst3em