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