symmetry in animals & bacteria

what is symmetry?

• most animals have bodies that show symmetry

• this means that the body can be cut into 2 halves that have a matching shape

asymmetrical

• no definitive shape

• cannot be cut into matching halves

spherical

shaped like a ball or sphere

radical symmetry

• has body parts that radiate from a center point

• meet their environment equally from all sides

• move quite slowly

• if they are sessile, their food must float or they must create water currents

bilateral symmetry

• 1 plane of symmetry

• concentration of nerves & sense organs at the anterior end

• food capturing structures are usually close to the head

• digestive, excretory, & reproductive organs are found closer to the posterior end

• a streamline body allows for faster movement

bilateral symmetry planes

• right & left side

• anterior end = head

• posterior end = tail

• dorsal surface = back

• ventral surface = front

bacteria structure

• unicellular prokaryotes

• lack organelles

• DNA is free in the cytoplasm (no nuclear membrane)

• 1 um in size (1 millionth of a metre)

shapes of bacteria

round: coccus

rod: bacillus

spiral: spirillum

arrangement of coccal bacteria

single cells: monococcal

pairs of cells: diplococcal

a string of cells: streptococcal

a bunch of cells (like grapes): staphylococcal