biology definitions

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simple tissue
a tissue comprises of a group of similar cells working together to perform a specific function
complex tissue
a tissue that is made up of a group of different cells working together to perform a specific function
organ
a group of similar or different tissues working together to perform a specific function
diffusion
the net movement of particles from a region of higher concentration to a region of lower concentration
osmosis
the net movement of water molecules from a solution of higher water potential to a region of lower water potential through a partially permeable membrane
plasmolysis
the shrinkage of cytoplasm & cell membrane away from the cell wall due to the loss of water when a living cell is immersed in a solution of lower water potential
active transport
the movement of particles from a region of lower concentration to a region of higher concentration through a partially permeable membrane

energy is required for this process
enzymes
biological catalysts made of protein that alter or speed up chemical reactions by lowering activation energy without themselves being chemically changed at the end of the reaction
denaturation
change in the active site of an enzyme or any other soluble protein

caused by high heat or chemicals such as acids and alkalis
photosynthesis
process in which chlorophyll absorbs light energy & converts it into chemical energy for the formation of carbohydrates from water & carbon dioxide

oxygen is released
photosynthesis word equation
carbon dioxide + water = light energy + chlorophyll = glucose + oxygen + water
Photosynthesis equation
6CO2 + 6H2O --> light energy + chlrohophyll --> C6H12O6 + 6O2 + 6H2O
digestion
process by which large food molecules are broken down into small, soluble & diffusible molecules that can be absorbed into the blood stream & body cells
physical digestion
mechanical breakdown of food into smaller parts to increase surface area to volume ratio to speed up enzyme reaction
chemical digestion
process whereby enzymes breakdown large food molecules into smaller, soluble molecules that can be absorbed into body cells
assimilation
process where some of the absorbed food substances are converted into new protoplasm or used to provide energy
peristalsis
rhythmic, wave-like contractions of the gut walls to mix & propel the contents along the alimentary canal
double circulation
the blood passes through the heart twice in one complete circuit
coronary heart disease
condition where the coronary arteries become narrow or blocked hence blood supply to the heart muscles is reduced
Phagocytosis
process of engulfing and ingesting foreign particles by phagocytes
Transpiration
the loss of water vapour from the aerial parts of the plant especially through the stomata of leaves
translocation
transport of manufactured food substances such as sucrose & amino acids in the phloem
respiration
oxidation of food substances with the release of energy in living cells for cellular activities
aerobic respiration
breakdown of glucose in the presence of oxygen with the release of a large amount of energy

carbon dioxide and water are released as waste products
Aerobic respiration equation
C6H12O6 + 6O2 = 6CO2 + 6H2O + large amount of energy
anaerobic respiration
breakdown of glucose in the absence of oxygen. less energy released compared to aerobic respiration
anaerobic respiration equation
human muscles:
glucose = lactic acid + small amount of energy

yeast:
glucose = ethanol + small amount of energy + carbon dioxide
oxygen debt
amount of oxygen required to breakdown the lactic acid produced in muscles during anaerobic respiration
Gaseous exchange
exchange of gases between an organism and the environment
excretion
removal of metabolic waste products & toxic materials from the body of an organism
homeostasis
maintenance of a constant internal environment
negative feedback
process where the body carries out a corrective mechanism in response to a stimulus to bring about the reverse effect of a stimulus, which on restoring the normal conditions, causes a feedback to the receptor to stop the corrective mechanism
stimulus
change in the environment that causes an organism to react
involuntary action
automatic bodily activities not under conscious control
reflex action
immediate response to a specific stimulus without conscious control
synapse
junction between 2 neurons or a junction between neurone & an effector such as a muscle or a gland
focusing
the adjustment of the lens of the eye so that clear images of objects at different dustances are formed on the fovea of the retina
hormone
chemical substance produced by an endocrine gland
carried by the blood
alters activity of 1 or more specific target organs & is then destroyed by the liver & excreted by the kidneys
endocrine gland
ductless gland that secretes chemical substances directly into the bloodstream
exocrine gland
gland that secretes chemical substances & has a duct which carries away its secretions
asexual reproduction
process resulting in the production of genetically identical offspring from one parent without the fusion of gametes
sexual reproduction
process involving the fusion of nuclei of 2 gametes to form a zygote resulting in the production of genetically unidentical offspring
gametes
reproductive cells containing haploid number of chromosomes
fertilisation
process involving fusion of haploid nuclei of male and female gametes. a diploid zygote is formed
self-pollination
transfer of pollen grains from the anther to the stigma of the same florwer or a different flower on the same plant
Cross pollination
transfer of pollen grains from the anther of one plant to the stigma of a flower in another plant of the same species
Menstruation
monthly discharge of blood and broken down uterine lining from the uterus via the vagina
ovulation
release of a mature egg from the ovary around day 14 of the mesntrual cycle
menstrual cycle
28 day cycle of events involving menstruation and ovulation which takes place in the female reproductive system. it is controlled by hormones
Implantation
process where an embryo becomes embedded in the uterine lining
mitosis
nuclear division such that the daughter nuclei contain the same number of chromosomes as the parent nucleus
meiosis
nuclear division such that the daughter nuclei contain half the number of chromosomes as the parent nucleus
Haploid
condition of cells that contain half the number of chromosomes as their parent cell
diploid
condition of cells that contain the full number of chromosomes in the body of an organism
Homologous chromosomes
chromosomes which exist in pairs and have the same sequence of genes

one chromosome in the pair comes from the male parent and the other from the female parent

each pair has the same shape, length and size
nucleotide
basic unit of DNA

made up of deoxyribose sugar, phosphate group and nitrogenous base
Base pairings
adenine + thymine
guanine + cytosine
gene
sequence of nucleotides occupying part of a DNA molecule

each carries a genetic code for the synthesis of a specific polypeptide
deoxyribonucleic acid
molecule that carries genetic information for the synthesis of specific polypeptides
chromatin
fine, thread-like structure comprising of a molecule of DNA wrapped around proteins
chromosome
made up of DNA
carry many genes along its length
rod-like structure visible in the nucleus during cell division
vector
an agent used to carry genes of one organism into another
eg: bacterial plasmid
gene
units of inheritance found on a particular position in a given chromosome

consists of a sequence of nucleotides that carries the code for the synthesis of a specific polypeptide
allele
one of the different forms of a gene

alleles of the same gene occupy the same relative position on a pair of homologous chromosomes
dominant
allele that expresses itself in the phenotype in both homozygous and heterozygous conditions
Recessive
allele that only expresses itself in the phenotype in the homozygous condition
codominance
the condition where both alleles express themselves in the phenotype under heterozygous condition
homozygous
an organism that has identical alleles for a particular phenotype
heterozygous
an organism that has different alleles for a particular phenotype
phenotype
expressed trait in an organism
genotype
genetic make-up of an organism
mutation
sudden or spontaneous change in gene structure or chromosome number

may be inheritable
variation
differences in a particular trait between individuals or the same species
Discontinuous variation
traits with limited variation in their phenotypes which are easily distinguishable

usually controlled by only 1 or a few genes

not affected by the environment

eg: blood group
Continuous variation
traits with phenotypes ranging from one extreme to the other

brought about by combined (additive) effects of many genes

affected by the environment

eg: height, skin colour
natural selection
process in nature which results in the best adapted organisms in a population surviving to reproduce. these organisms pass on more of their genes to the next generation compared to others that are poorly adapted & eliminated subsequently
evolution
process by which the present complex forms of living organisms have arisen from simpler ancestral forms

possible mechanism for evolution
artificial selection
method used by humans to reproduce plants & animals with desirable qualities
habitat
place where an organism lives
population
group of organisms of the same species living in a particular habitat
community
all the populations of various organisms living and interacting with one another in a habitat
ecosystem
interaction of living organisms in a community and their physical environment
biotic environment
all living things that an organism interacts with
abiotic environment
physical factors eg: light and temperature, in the environment
producer
can absorb and convert light energy to chemical energy and store chemical energy in the form of food during photosynthesis
consumer
organism that obtains its energy and nutrients from other organisms it feeds on
decomposer
breaks down dead organisms and waste matter, taking in some energy and nutrients while releasing the rest to the environment
food chain
series of organisms through which energy is transferred in the form of food
food web
made up of 2 or more food chains linked together
trophic level
each stage in a food chain
pyramid of numbers
shows number of organisms present in each trophic level at a particular time
pyramid of biomass
shows (dry) mass of organisms present in each trophic level at a particular time
pyramid of energy
shows total energy present in each trophic level over a period of time
carbon sinks
natural systems that take up and store more carbon from the atmosphere than they release

eg: forests and oceans
carbon sources
natural systems that release more carbon to the atmosphere than they store
bioaccumulation
process whereby chemicals are not excreted but accumulated in bodies of organisms. these chemicals are then passed along food chains and become more concentrated in the bodies of final consumers
bioamplification
buildup of concentration of chemical substances eg: pesticides in the bodies of organisms along trophic levels of a food chain
transgenic organism
an organism with genetic characteristics that have been altered by the insertion of a modified gene or a gene from another organism using the techniques of genetic engineering
absorption
process where small, soluble molecules pass through the walls of the digestive system through the process of diffusion, osmosis and active transport, where they enter the bloodstream to be carried to other parts of the body
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