BIO 193 Exam II

etiolation

developmental pattern in darkness

de-etiolation

greening response in light

dark-grown vs light-grown seedlings

• dark-grown seedlings: prioritize stem elongation

• light-grown seedlings: produce expanded green leaves and stronger roots

general model of signaling

1. reception: detection of stimulus

2. transduction: conversion of external cues to internal signal

3. response: developmental outcomes

mechanisms of de-etiolation

• phytochrome acts as the receptor

• cGMP and Ca2+ act as second messengers

primary driver of plant greening

gene expression changes

plant hormones as chemical communication

• act at very low concentrations

• one hormone can have multiple effects

• one process can be controlled by multiple hormones

• hormone interactions matter more than isolated hormones

auxin

mobile signaling hormone that regulates growth, development, and environmental responses

phototropism

coleoptile tip senses light and triggers a mobile signal hormone (auxin) to move down the shaded side to cause differential growth

differential growth

fundamental process that causes curvature by growing one side of an organism, tissue, or cell faster than the opposite side

auxin mechanism

increases the activity of proton pumps and reduces the cell wall pH

expansins

loosens the cell wall/makes it more flexible to increase water uptake and turgor, which drives elongation of the cell

• activated by reduced pH in cell wall

apical dominance

apical bud suppresses the growth of axillary buds making plant grow upward rather than outward

• dominance maintained by auxin which moves downward and prevents side shoot development

strigolactones

plant hormone that represses bud growth

cytokinins

plant hormone that counters repression of bud growth and promotes branching

gibberellins (GAs)

plant hormones that regulate growth and development

• released by embryo

endosperm function during germination

converts starch to sugar for embryo energy

aleurone

aleurone: nutrient-dense outermost layer of endosperm cells

• makes alpha amylase

scutellum

scutellum: shield-shaped single cotyledon

• transfers nutrients from endosperm to embryo

GA (gibberellins) and ABA (abscisic acid) balance

helps determine germination vs dormancy

phototropism

directional growth of an organism in response to light

• occurs when the tip is separated by a permeable barrier, but not an impermeable barrier

responses to phototropism with cap

tip removed: no response

opaque cap on tip: no normal bending

transparent cap on tip: bending remains

opaque shield on lower region: bending occurs

photomorphogenesis

effects of light on plant morphology

photoperiodic flowering responses

• short-day plant: flowers only when the light period is shorter than a critical length

• long-day plant: flowers only when the light period is longer than critical length

• day-neutral plant: flowers based on age rather than the length of day

white light

mixture of all wavelengths of visible light

red/far-red reversibility

• short day plant: red night break prevents flowering, and far-red reverses it

• long day plant: red night break induces flowering, and far-red reverses it

phytochrome

photoreceptor proteins that act as light sensors

• lines up plant’s internal timing system with the outside world

grafted short-day and long-day plant

leads to both flowering under short-day conditions

florigen

mobile signal that links to the FT protein and travels to the shoot apical meristem to initiate flowering

kindoms division

based on on fundamental differences in cell structure, cell number, and mode of nutrition

prokaryotic cell vs eukaryotic cell

prokaryote: no nucleus or organelles

• archaea and bacteria

eukaryote: membrane bound nucleus and organelles

• protista, plantae, fungi, and animalia

multicellular organisms

contain cells specialized to perform certain functions and are often organized into tissues and organs

autotrophs vs heterotrophs

autotroph: produce their own food using sunlight or chemical energy (producers)

heterotrophs: consume other organisms for energy (consumers)

• herbivores, carnivores, and omnivores, includes both fungi and animalia

modes of digestion in heterotrophs

fungi: digest food externally and absorb the digested food

animals (some exceptions): ingest and digest food internally

common features of animals

• multicellular, heterotrophic, eukaryotes that ingest and digest their food

• lack a cell wall

• capable of moving (at some point during their lives)

• have regulatory genes called Hox genes

• have structural genes

Hox genes

involved in the development of the body plan in animals

animal reproduction

most reproduce sexually

• dominant diploid stage

• male produce motile, flagellated sperm, which fertilizes non-motile egg

physiology

study of how animals work

• molecular and protein interactions are responsible for cellular processes which determine tissue and whole organ function

animal groups distinction

• animal body plans (symmetry), development, and tissue organization

• molecular data (DNA)

spherical symmetry

occurs when any plane passing through the center divides the body into mirror image halves

• mostly in protists

radial symmetry

applies when more than two planes passing through the longitudinal axis can divide the organism into mirror image halves

bilateral symmetry

found in organisms where one plane can pass through the organism dividing it into right and left halves

• associated with cephalization, the differentiation of a head

cephalization

nervous tissue, sense organs, and often the mouth are located in the head

bilaterally symmetrical regions

transverse plane: anterior-posterior

frontal plane: dorsal-ventral

sagittal plane: left-right

cleavage

rapid division of mitotic cells that occurs in the early embryo following fertilization

blastula

hollow sphere of cells surrounding a fluid-filled cavity called the blastocoel, formed by cleavage

gastrulation

blastula reorganizes into a gastrula with different layers of embryonic tissues

ectoderm

covers outer surface (outermost germ layer in an animal embryo)

endoderm

innermost germ layer and lines the developing digestive tube

diploblastic

animals have only an ectoderm and endoderm

triploblastic

animals also have an intervening mesoderm layer (instead of just an ectoderm and endoderm)

mesoderm

middle germ layer that forms muscle and most internal organs

gut

body cavity that forms from the archenteron during gastrulation

blastocoel

fluid-filled cavity that forms within the blastula and persists in some, but usually
fills with mesoderm

pseudocoel and coelom

fluid filled body cavities that cushion organs and provide support

acoelomates

triploblasts that lack a body cavity or coelom

pseudocoelomates

cavity lining has one mesodermal and one endodermal face

coelomates

organs suspended in cavity lined by mesoderm

• cavity fluid may act as a hydrostatic skeleton (support and enables movement)

two animal groups distinguished by features of early development

protostome and deuterostome

• differ in cleavage pattern, mode of coelom formation, and fate of the blastopore

protostomes

fate of the blastopore: becomes the mouth

mode of coelom formation: schizocoelous

cleavage pattern: spiral (diagonal to midline) and determinate (fate of each cell decided early)

schizocoelous

solid mass of mesoderm splits down the center and forms coelom

deuterostome

fate of the blastopore: becomes the anus

mode of coelom formation: enterocoelous

cleavage pattern: radial (perpendicular or parallel to midline) and indeterminate (each cell retains potential to become entire embryo)

enterocoelous

mesoderm buds from archenteron (digestive track), forms cavity

animal phylogeny hypotheses

hypothesis #1: based mainly on morphological and developmental comparisons

hypothesis #2: based mainly on molecular data, DNA sequence similarity

lophotrochozoans

clade of protostome animals

• feed with a ciliated lophophore

• have distinct trochophore larval stage

ecdysozoans

group of protostome animals

• secrete a hard exoskeleton

• must molt by ecdysis to accommodate growth

eumetazoa

clade of animals with true tissues

bilateria

clade most animal phyla belong to

basal animals

earliest-diverging lineages in the animal kingdom (often have simpler ancestral traits)

• ex: sponges

porifera (sponges)

• most species are marine (~5000) but some are freshwater (~150) at all depths

• few predators due to containing distasteful toxins

  • some can sequester these toxins and use them to deter their own predators

sponges lack…

‘true tissues’

• no circulatory system

• no respiratory system

• no digestive system

• no nervous system

• no muscles

sponges structural organization

assemblages of cells embedded in a protein matrix (mesohyl) and supported by a skeleton of needle-like structures (spicules)

boring sponge

parasitic sponges that attach to hard surfaces to absorb nutrients from the animal

• often kills the host and gives the sponge a surface to live on

sponge reproduction

asexually: fragmentation, budding, or regeneration

• freshwater species can produce ‘spore’-like gemmules which survive harsh conditions by entering a period of dormancy

sexually: sequential hermaphroditism

• have male + female parts but function first as one sex, then as the other

choanocytes

specialized flagellated cells that line the inner chambers of sponges and give rise to eggs and sperm

• sperm are released into the water and eggs are retained within the sponge

sponges cell cycle

• filtering cells divide every 5-6 hours

• shed cells very rapidly

  • shed sponge cells are an important food source for many organisms

cnidaria (corals, anemones, jellies and hydras)

diploblastic with radial symmetry

• two variations of body plan: sessile polyp and motile medusa

cnidaria nervous system

simplest form (nerve net) which allows them to detect and respond to stimuli

cnidaria muscular system

simple system where cells of the gastrovascular cavity and epidermis can contract

hydrozoans

alternate between polyp and medusa phases

anthozoans

corals and anemones - “flower animals”

coral mutualistic relationship

contain endosymbiotic brown algae called zooxanthellae

• zooxanthellae provide food for the coral (boost in nutrients —> grows quickly)

• coral provides a safe home for zooxanthellae to live in

coral polyps

absorbs calcium carbonate out of the water and secretes it to build the reef

• build a calcium carbonate cup (corallite) to live in

coral reef

formed by ‘hard’ corals laying down a calcium carbonate skeleton

• one of the most productive ecosystems in the world even though the water is nutrient-poor

three types of reefs

1. fringing: grows close to shore

2. atoll: a ring of coral that surrounds a lagoon, often grows on a submerged mountain or volcano

3. barrier: also grows close to shore but has a lagoon separating it from the shore

coral requirements

• clear, warm water

• full strength seawater

• regions with some wave action (to avoid being covered in silt - interferes with photosynthesis)

• subtidal (to avoid dying from long exposure to air)

cnidaria prey

• capture with a ring of tentacles around their mouth

  • then digest them in the gastrovascular cavity

• harpoon prey by launching cnidae (venomous organelles) contained in specialized cells (cnidocytes)

ctenophora (comb jellies)

diploblastic with radial symmetry

• have 8 rows of cilia used for locomotion (bioluminescent combs)

• lack cnidae, but have sticky tentacles to capture prey

two general types of physiological signals cells use

electrical signals

chemical signals

• secreted by cells into extracellular fluid

• responsible for most communication within the body

four basic methods of cell to cell communication

1. gap junctions

2. contact-dependent signals

3. autocrine and paracrine signals

4. long-distance communication

gap junction communication

connexins (membrane spanning proteins) form a channel between two adjacent cells

• can be opened and closed, allowing small molecules + electrical signals to pass

contact-dependent communication

surface molecules on one cell membrane bind to surface molecules on another cell membrane

• CAMS (contact adhesion molecules) role: cell to cell adhesion, connect proteins in different cells, send signals from cell to cell

autocrine and paracrine communication

chemicals (ligands) can be released from one cell and diffuse through the extracellular fluid

• autocrine: act on the same cell that released the ligand

• paracrine: act on nearby cells

endocrine system (long-distance communication)

hormones are released from endocrine cells and enter the blood where they can travel long distances to act on cells which have a receptor for that hormone

exocrine glands

release their secretions into ducts that lead to a target cell

neurohormones (long-distance communication)

chemicals released by neurons into the blood for action at distant targets

neurotransmitters

chemicals secreted by neurons that diffuse across a small gap to the target cell

• neurons use electrical signals as well

singaling pathways

signal molecule binds to receptor protein activates intracellular signal molecules alter target proteins create response

platyhelminthes (flatworms)

triploblastic, bilaterally symmetrical acoelomates

• live in marine, freshwater and damp terrestrial habitats

planarians (turbellarians)

• nearly all free living and mostly marine

• move by using cilia on their ventral surface

• have a more specialized nervous system than cnidarians