BIO 193 - Exam II

hox genes

subset of homeotic genes; control genes that determine the identity and position of body parts during embryonic development

homeobox

DNA sequence → makes homeodomain (protein) → gene expression

tissues

a linked group of cells that share a common structure and function

cleavage

rapid mitosis of the zygote, without the embryo growing bigger

blastula

hollow formation of cells after cleavage (rapid mitosis)

gastrulation

formation of three germ layers (ectoderm, mesoderm, endoderm)

metamorphosis

major change in an animal's body form and structure as it develops from a young stage into an adult

body plan

• the basic structure of features related to form + development

• animal classification based on;
  - presence or absence of tissues
  - radial or bilateral symmetry
  - partial or complete body cavity

radial symmetry

exists in organisms that be split into a mirror image

radial symmetry

the body can be divided into multiple planes (central axis)

bilateral symmetry

the body can be divided into two matching mirror-image halves by one specific plane (left and right)

anterior

head

posterior

tail

dorsal

back

ventral

belly

cephalization

concentration of sensory organs and nervous tissue toward the head

acoelomates

animals that do not have a fluid-filled body cavity (coelom) between the digestive tract and body wall

pseudocoelomates

animals with a body cavity (pseudocoelom) that is partially lined by mesoderm tissue

coelomates

animals with a body cavity (coelom) that is completely lined by mesoderm tissue

protostome development

the blastopore becomes the mouth

deuterostome development

the blastopore becomes the anus

radial cleavage

cell divisions are parallel or perpendicular to midline

spiral cleavage

cell divisions are diagonal/angled to midline

indeterminate cleavage

early cells can still develop into a complete organism

determinate cleavage

early cells have a fixed developmental fate and cannot form a complete organism

schizocoelous

the coelom forms when a solid mass of mesoderm splits open to create the body cavity

enterocoelous

the coelom forms as pouches that bud off from the digestive tract (archenteron)

lophophore

a crown or ring of tentacles around the mouth used for feeding

trochophore

a free-swimming larval stage with bands of cilia used for movement and feeding

hormones

chemical signals that send messages through the body

phytohormones

plant hormones that stimulate or inhibit growth, development, responses to the environment (examples: auxins, cytokinins, gibberellins)

tropism

growth response resulting in curving of plant organs

• positive = toward the stimulus

• negative = away from the stimulus

  • phototropism: response to light

  • gravitropism: response to gravity

  • thigmotropism: response to touch

auxin

plant hormone that promotes cell growth by cell elongation

acid growth hypothesis

auxin (hormone) → acidic cell walls → cell walls loosen → cells grow longer

apical dominance

the main stem grows and prevents side branches from growing (due to auxin)

ethylene

a gaseous plant hormone; promotes fruit ripening, leaf aging, and dropping

convergent evolution

different ancestors; similar traits

divergent evolution

common ancestor; different traits