biology
characteristics of life
mrs H Gren
Viruses show some of the characteristics, do not carry out biochemical reactions independently of host cell and are not made of cells, so not seen as living
Movement
Respiration
Sensitivity
Growth
homeostasis
Reproduction
Excretion
Although not all life can move in sense of locomotion (moving the whole organism from place to place), all cells can move components around inside the cytoplasm
Some plants are able to move tissues or organs (stomata, venus fly trap), these movements are reversible so considered movement, but the growth of a plant towards the sun is irreversible and just a growth response, s is not
RELEASE of energy through oxidation of an energy source
aerobic
anaerobic
energy source + oxygen -------> water + carbon dioxide + energy
energy source ------> lactic acid/etahnol + carbon dioxide + energy
NOT BREATHING
takes place in cytoplasm for bacteria, mitochondria for eukaryotes
Ability to respond to changes in surroundings
more common
occurs in some bacteria, some fungi, and to a small extent in human muscles
nervous systems or hormones for animals
for plants generally takes form of changes in pattern of growth
unicellular organisms usually confined to moving in response to stimuli such as light or chemicals
can be done by either enlarging cells by increasing volume of cytoplasm or cell division , increasing the number of cells in the organism
multicellular organisms do both
when single celled organisms divide is not growth as two daughter cells considered separate organisms
most organisms reproduce sexually, leading to variable offspring, some reproduce asexually, leading to offspring that are genetically identical to the parent plant
NOT EGESTION, which is the removal from the body of undigested food in the form of faeces
removal of waste products from an organism
removal of things PRODUCED by the organisms
e.g. urea and carbond dioxide
need to be removed as often toxic in high quantities
Nutrition
obtaining of chemicals for either use in respiration to release energy or for use in the building of new molecules with which to construct new cells
two types
autotrophic
heterotrophic
synthesise food molecules from simpler molecules e.g. photosynthesis
use pre-existing food molecules which are then digested and used
maintenance of constant internal conditions despite changes in external environment
humans can regulate concentration of blood, temperature, blood pH and concentration of mineral ions
unicellular organisms can still regulate chemical composition of cytoplasm eg pH
One extra feature
Nucleic acids/genetic material
all living organisms contain DNA in cells
in prokaryotes DNA is single loop located in cytoplasm, in eukaryotes DNA is packaged using proteins into multiple linear strands called chromosomes
molecule which provides instructions for how a cell is built and functions, molecular code which determines which proteins are synthesized by the cell
precise type of DNA that a cell contains determines which organism the cell belongs to
also RNA
contain nucleic acid, when a virus infects a cell, it injects the nucleic acid into the cell and the infected cell then uses them to make more copies of the virus proteins