Biol 371 Flashcards
1
Q
What are protists?
A
Unicellular eukaryotes
2
Q
Did plants and animals have a common multicellular ancestor?
A
No. They had a common unicellular eukaryotic ancestor.
3
Q
Did plants and animals diverge before engulfing mitochondria and chloroplasts or after? and why.
A
They diverged after mitochondria but before chloroplasts as we see both with mitochondria but animals do not have chloroplasts.
4
Q
When did eukaryotes evolve?
A
About 2.5 mya
5
Q
When did prokaryotes evolve?
A
About 3.5 bya
6
Q
How do prokaryotes and eukaryotes differ in terms of their cytoskeleton?
A
Eukaryotes - well developped, internal, complex, allows for movement within cell as well as the cell itself
Prokaryotes - use diff. proteins, not able to be as flexible with movement within cells
7
Q
How do the genomes of prokaryotes and eukaryotes differ?
A
Prokaryotes - circular DNA, loose in cell
Eukaryotes - membranne bound nucleus, multiple linear chromosomes
8
Q
How do ribosomes differ between prokaryotes and eukaryotes?
A
Prokaryotes use 60S ribosomes, eukaryotes use 80S ribosomes.
9
Q
What is a large advantage for eukaryotes over prokaryotes?
A
Eukaryotes have internal membranes which gives them a larger surface area for chemical processes. This allows them to become larger in volume but not much larger in surace area.
10
Q
Describe sexual reproduction in eukaryotes
A
Combination of genes to produce unique offspring thereby increasing genetic diversity. This is a slow process.
11
Q
Describe reprodution in prokaryotes.
A
Prokaryotes reproduce asexually meaning that they are exact copies of the first cell. This is a fast process.
12
Q
Where is the axoneme located?
A
In eukayotic flagellum
13
Q
What makes up the axoneme?
A
Nine pairs of microtubules. 8 in a circle conected with dynein arms and 1 in the middle.
14
Q
What does the mitochondria do?
A
Oxidation phosphorolation forming ATP
15
Q
Why do we believe that eukaryotes engulfed prokaryotes forming mitochondria and chloraplates?
A
Both have their own circular DNA separate from the cells DNA in the nucleus. They have a double membrane, 1 that was their own and 2 the one that formed around it during engulfment. Use of a 70S ribosome and not the 80S ribosome.
16
Q
What types of cells are not multicellular?
A
Bacteria, prokaryotes, archaea
17
Q
Why is there such a large gap between the evolution of prokaryotes and eukaryotes?
A
Cyanobacteria were the first to use CO2 and produce O2. Iron in the earth used the O2 until it was all rusted at which point there was an increase in atmospheric O2 allowing for eukaryotes to evolve.
18
Q
Why are the three theories of origins of multicellularity?
A
- Symbiotic theory
- Syncytial theory
- Colonial theory
19
Q
What are dis-/advantages of the symbiotic theory?
A
Diff. species came together to form collective group with each species completing a differnet task.
Only problem is how do we explain all cells of a multicellular organism having the same DNA?
20
Q
What are the dis-/advantages of the syncytial theory?
A
One cell broke nuclei into multiple nuclei and each section was to accomplish a diff. task.
There is not enough evidence supporting this theory.
21
Q
What are the dis-/advantages of the colonial theory?
A
Grouping of one species working together to complete different tasks (specializing).
There is evidence that this happens but there is no evidence that they eventually form ONE functioning unit
22
Q
List 3 advantages of being multicellular.
A
- division of labour and economy of scale
- increase size
- complexity
23
Q
List 4 disadvantages of being multicellular.
A
- surface/volume relationship
- interceullular communication
- cell adhesion
- structure and support
- homeostasis
- reproduction and growth
24
Q
What is the name of animal and fungi ancestor?
A
Opisthokonts
25
What is the name of plant ancestors?
Archaeplastida
26
What does opisthokonts include?
animals, fungi and choanoflagelates
| single, posterie (opisthios) flagellum (kontos)
27
How is it belived that opisthokonts evolved?
From a colony of choanoflagellates that formed a two-layered animal with a sac-within-a-sac body plan (a digestive cavity) due to envagination of one side of circular colony.
28
What are two identifiers of animals that no other organism has?
- certain extracellular matrix molecules (proteoglycans and collagen)
- tight/septate junctions for communication between cells ( desmosomes and gap junctions)
29
What does the archaeplastida include?
land plants, red and green algae
30
When did land plants first evolve?
490 mya (later than animals)
31
Name three main differences between plant and animal cells.
- cell wall (support and transport)
- vacule (turgor pressure)
- chloroplats (photosynthesis)
32
Explain photoautotrophic
using light as an energy source and being able to fix inorganic carbon
33
Explain chemoheterotrophic
using other organisimes as an energy and organic carbon source
34
How did plants overcome their limit on movement?
- ability to grow in different directions
- phototrophic (orient themselves to light)
- move in response to physical stimuli (venus fly trap)
- disperse by pollen/seeds
35
What are some disadvantages of animals having to be mobile?
- muscle
- well developed senses
- limbs/joints
- high metabolic rate
36
What is a hydrostatic skeleton?
fluid filled system that uses pressure
37
Give examples of sessile animals.
All aquatic
| -barnacle, coral, mussels, tube worms
38
How did sessile animals conserve energy?
They are filter feeders and allow the currents to bring them food. They also lost the head portion.
39
What was the first divergence of the colonial choanoflagellate?
Nerves. No nerves are the porifera (no true tissue only non-specialized cells) and nerves lead to radiata and bilateria
40
What are the three types of body symmetry?
aymmetrical (no symmetry)
radial (central axis with multiple symmetries)
bilateral (only one symmetry)
41
What are the three tissue layers?
- Ectoderm (di, tri)
- Endoderm (di, tri)
- mesoderm (tri)
42
What are the three body cavity types?
- acoelomate (no body cavity just tissue between gut and body wall)
- pseudocoelomate (fluid filled cavity between gut and body wall)
- -(eu)coelmoate (completely lined by mesoderm derivative)
43
What are the two types of clevage?
Protosomes
| Deuterostomes
44
What are the characteristics of protosomes
- determinate
- schizocoelous coelom
- spiral clevage
- mouth forms first then anus Mouth formed by the blastopore (proto= first stoma=mouth)
- ventral (nerve cord surronds digestive tract anteriorly)
45
What are the characteristics of deuterostomes?
- indeterminate
- enterocoelous coelom
- radial clevage
- anus forms first then the mouth (deutero=second stoma= mouth)
- dorsal (hollow nerve cord. brain doesn't surround digestive tract)
46
What are the two sub classes of protosomes?
Lophotochazoans
Ecdoysozoans
(refer to feeding system)
47
What is the difference between medusa and polyp forms?
Medusa is mobile and the moth faces down.
| Polyp is sessile and mouth faces up
48
What is the phylum for flat worms?
platyhelminthes
49
What is ecdysis?
Shedding of the exoskeleton in order to grow larger.
50
Describe the phylum Rotifera.
The one with the rotating drill like structures called corona.
51
What two phylum are included in the Ecdysozoans? And what is a defining feature?
Phylum Nematoda
Phylum Arthropoda
they both have an external cuticle for protection. All bilaterally symmetrical and triploblastic.
52
What model organism is included in the phylum Nematoda?
C. elegans.
53
What are three common features of arthropods?
- exoskeleton
- jointed legs
- segmented body
54
What are the two phylum of deuterostomes?
- phylum Echinodermata
| - phylum Chordata
55
What is unique about the phylum Echinodermata?
They are bilateral larvae but are pentaradiate symmetry as adults. Also you can cut in half and they will become two organisms.
56
What are the 4 characteristics of the phylum Chordata?
- notochord (flexible rod for muscle attachment)
- dorsal, hollow nerve cord
- gill slits
- segmented muscles with post anal tail
57
What are the three sub divisions of the phylum Chordata?
- cephalochordata
- urochordata
- vertebrata
58
What three characteristics do plants share?
- primary cell wall
- cellulose fibers in matrix of hemicellulose
- rigid but flexible
59
What in plants make them hard to digest?
cellulose
60
What will happen to a plant if it has very high hemicellulose?
It will be easier to degrade
61
Where do you find the xylem and sclerenchyma cells?
In the secondary cell wall.
62
What are some characteristics of the cell wall?
- cellulose is anchored with lignin
- stronger more rigid
- waterproof barrier
- not all cells have secondary cell walls, just the ones that support the rest of the plant
63
What is the purpose of lignin?
Lignin is hydrophobic that forms covalent bonds with the primary cell wall to strengthen the plant. Without lignin the plant would fall over.
64
Does the cell wall provide the rigid support the plant needs?
No it is the pressure from the vacule that makes it rigid.
65
Do vacules have low or high solute concentration?
High solute concentration.
66
What happens to a plant cell in an hypotonic solution?
The solute concentration is higher in the solution and so by osmosis water moves into the cell vacule causing cell the be turgid.
67
What happens to a plant cell in an hypertonic solution?
Water leaves the cell vacule to balance solute concentration. This causes the cell to be PLASMOLYZED.
68
What are two was of classifying land plants?
- Vasculature
| - Seeds
69
What makes up the vascular bundles?
- xylem
- phloem
- parenchyma cells
- fiber cells (sclerenchyma cells)
70
What do the xylem cells do?
Water transportation. Dead at maturity. Has secondary cell wall strengthened by lignin.
71
What do phloem cells do?
Sugar and other solute transportation.
72
What do the sclerenchyma cells do?
Provide rigid support to xylem and phloem.
73
When do we see land plants starting to form?
475 mya
74
When do vascular plants form?
425 mya
75
When do seed plants start to be seen?
305 mya
76
What do we call non-vascular plants?
Bryophytes
77
What do the Bryophytes include?
mosses, liverworts and hornworts
78
What are the two types of seedless land plants?
Lycophytes
| Pterophytes
79
What are the two types of plants with seeds?
Gymnosperm
| Angiosperm
80
What are common characteristics of non-vascular plants?
- haploid generation is dominant
| - requires water for fertilization
81
What does the word POIKILOHYDRIC mean?
poikilo= variable hydric=water
They can not control internal water content. If environment has a drought they dry out but will survive. They are drought tolerators.
82
Is the sporophyte haploid or diploid?
Diploid
83
What does the sporophyte (2n) make and how?
Spores (n) through meiosis
84
What does the gametophyte make and how?
Multiplies gametes (n) through mitosis.
85
How does the sporophyte form in moss?
It is the zygote which will later release spores.
86
What are microphylls? And which plants are they found in?
A microphyll is a narrow stem with ONE vein of vascular tissue. Lycophytes (pete moss)
87
What are megaphylls?
Broad leaf with many veins. Found in all other vascular plants.
88
In ferns (Pterophyta) where are the sporangia found?
Lower surface of leaf in groups called a sori.
89
In ferns which stage is dominant?
Diploid- sporophyte
90
What is antheridiogen?
It is a pheromone that promotes other gametophytes to produce sperm not eggs to increase the chances of cross fertilization and increase genetic diversity.
91
How can you tell which is the dominant phase?
The one that is completing the photosynthesis and supporting the other.
92
What are the two types of seed plants?
Angiosperms and Gymnosperms
93
What are other names for the pollen and female spores?
Microspore and megaspore respectively
94
What is a large difference between a megaspore and a microspore?
Microspore will creat 4 viable gametes whereas the megaspore will create 4 cells but only one becomes the gamete.
95
Why doesn't pollen have flagella?
Pollen is moved by air and not water; because of this is not not need to be motile in the same sense they have wing type structures instead
96
How does the ovule differ from seedless plants?
The female gamete remains connected and protected by the sporophyte and once the ovule is fertilized it seals up and becomes the egg.
97
What is the cotyledon?
The cotyledon is on the embryo that looks like fingers
98
What are advantages of seeds?
- protected from environment
- can travel far from parent tree
- dormancy is the greatest adaptation over animals.
99
What is the difference between monocots and eudicots?
```
Monocot
- single cotyledon
- parallel-veined leaves
- vascular bundles scattered
- flower petals in multiple of three
Eudicots
- reticulate veins
- central core of vascular tissue in stem
- flower part in fours or fives
```
100
What are advantages of angiosperms over gymnosperms
- better vessel elements
- more efficient phloem due to companion cells
- ovary is now protected by fruit
- double fertilization for produce embryo and endosperm
101
What are the challenges of life on land?
- desiccation
- respiration
- reproduction
- locomotion
- senses
102
Why do we believe anthropods were the first animal on land?
- exoskeleton
- jointed limbs
- multiple apendiges
103
What adaptations do land plants have to overcome the challenges of life on land?
- waxy cuticle
- stomata
- vascular tissue
- root system
104
How does the cuticle on plants prevent water loss?
The cuticle is hydrophobic
105
What synthesizes the cuticle?
The epidermal cell
106
What part of the epidermal does the cuticle attach to?
Pavement cells
107
When is the stomata open and when is it closed?
```
Flaccid = closed
turgid = open
```
108
What plants are tracheids found in?
Gymnosperms and ferns
109
What plants are vessels found in?
Angiosperms
110
How do tracheids and vessels differ?
Tracheids
- narrow
- water must pass through primary cell wall
Vessels
- shorter and wider
- both primary and secondary cell wall has gaps to facilitate water movement
111
What are ways animals decrease water loss on land?
- cuticle/ skin
- avoid hot/dry environments
- replace water by drinking
- concentrate urine to lose less water
112
What is aestivation?
Animals that dry out but are still alive
113
What are spiracles?
Opening of trachea at body surface
114
How does the rotifer reproduce in unstressed environment?
An adult female will produce a diploid egg through mitosis and the egg will grow and develop through mitosis.
115
How does the rotifer reproduce in stressed environment?
An adult female will make a haploid egg through meiosis. Through mitosis the egg will from an adult male. This male will make haploid sperm. The sperm and the haploid egg will form a zygote that can survive until favorable conditions are met.
116
How does temperature affect cells?
```
Freezing = lysed cells
heat = denatured proteins
```
117
How do animals overcome hearing on land?
Use fluid in the ear and the tympanal organ to detect vibrations.
118
What are the ways to support heavy body weight?
- skeleton for muscle attachment
- thick robost limbs
- rib cage to support organs
119
How do aquatic animals excrete ammonia?
Diffusion into surrounding water
120
How to vertebrates excrete ammonia?
Turn ammonia into urea with is less toxic and so does not need to be diluted as much
121
How do eggs and invertebrates excrete ammonia?
Change ammonia into uric acid crystals
122
What are the three systems of body weight support structures?
- Sprawling
- erect
- pillar-erect (extinct)
123
What are challenges of living in water?
- water is dense and harder to move through than air
- water has low oxygen content
- water has high thermal conductance
124
How do aquatic endotherms deal with the temperature of the water?
Since they generate heat and this is very costly they breath air to increase the availability of oxygen in their system rather than get it from the water
125
What are three ways to conserve heat in water?
- insulate (blubber, fat)
- respiratory medium (breath air instead)
- countercurrent heat exchange (as warm blood moves toward the surface it gives its heat to cold blood moving to body core. Requires parallel vessels)
126
Describe the negative feedback loop of homeostasis.
There is a setpoint to which it wants to be. This communicates with the integrator. The integrator will give negative feedback to the metabolic process. This occurs when the product triggers the sensor which communicates with the integrator.
127
What are some substances that need to be maintained?
- nutrients
- gasses
- pH
- ammonia
- water
- volume/pressure
- temperature
128
What is diffusion?
Moving from high to low concentration
129
What is Frick's law?
Rate=DAdC/dX
130
What are the three possibilities of comparing two solutions to each other?
- Hyperosmotic (the cell has lower solute concentration than the ECF)
- Hyposmotic (the cell has higher solute concentration than ECF)
- Isosmotic (the two solutions have the same concentration)
131
How do you calculate water potential?
Water potential = - osmotic + hydrostatic
osmotic = drawing water in
Hydrostatic = pushing water out
132
How does water potential affect animals?
Only concerned with osmotic because if the cell swells it will burst and if the cell shrinks it will die
133
How does water potential affect plants?
Need to look at both osmotic and hydrostatic effects since there is a cell wall on plants that the vacule can push against and push water out.
134
What are the two ways animals can osmoregulate?
1. Osmoconformers
| 2. Osmoregulators
135
What do osmoconformers do?
Adjust osmotic strength of cells to match environment.
136
What do osmoregulators do?
Adjust osmotic strength of extracellular fluid to match cells
137
What are the three steps in excreting waste?
- Filtration
- Secretion
- Reabsorption
138
What is the main objective during the excretion process?
Create a concentrated product for removal with least amount of water possible.
139
Why is circulation important?
- communication
- nutrient movement
- diffusion is not enough in larger animals
140
How does the metabolic rate compare in animals to plants?
Animals have high metabolic rates while plants have low metabolic rates.
141
What are the three types of muscle in animals?
- Skeletal
- Smooth (provides tension around blood vessels)
- Cardiac muscle
142
What does smooth muscle do?
Provides tension around blood vessels
143
What is important about the heart?
It increases the pressure of the bulk flow as vessels reduce pressure due to resistance.
144
How do single circuit work?
Passes through the heart only once then must go by gills and body before returning to the heart.
- No lungs
145
How does variable circuits work?
They pass through the heart twice before going through the rest of the body. The first time they go to the gills or lungs. There is no division between the two sides of the heart.
146
How does double circuit work?
Passes through the heart twice and is separated between the two ventricles. The first pass is to the lungs to collect oxygen while the second pass is to the rest of the body.
147
What do arteries do?
Carry fluid away from heart
148
What do Veins do?
carry blood to the heart
149
What does blood contain?
Plasma - water, ions, proteins, gas
Erythrocytes
Leukocytes
Platelets
150
What is an open circulatory system?
The blood moves from the heart to the cells. Bathing them before returning to the heart. Direct contact with cells.
151
What is a closed circulatory system?
The blood moves from the heart through vessels then through small capillaries. The substances then move from the blood into the ECF before going into the cell. No direct contact.
152
Why must plants and animals breath?
krebs cycle and oxidative phosphorylation
- consume oxygen and release carbon dioxide
photosynthesis
- consumes CO2 and releases O2
153
What are the four steps of gas exchange in animals?
1. Ventilation
2. Diffusion
3. Perfusion
4. Diffusion
154
What is required for gas exchange on land?
- large surface area (surface to volume ratio)
- moist to dissolve gas
- thin so easy to diffuse
155
What are spiracles?
trachea openings on the surface
156
How many essential elements do plants require?
17
157
What are macroelements?
they are essential in large quantities
158
What are microelements?
they are essential in small quantities
159
What is humus?
decomposing organics
160
What charge is humus and clay?
negative
161
Why is it beneficial to have clay and humus in the soil?
Since they are both negative they hold water better allowing for a better soil solution for plant uptake
162
What is soil solution?
It is the water that remains after gravity that has dissolved substances and coats soil particles
163
How do plants acquire cations?
They release either H+ or H2CO3 (which dissociates into HCO3- and H+) to exchange the cations attached to clay particles
164
How is carbonic acid formed?
respiring root cells
165
How do plants acquire anions?
simple diffusion
166
Why is it more difficult to acquire anions compared to cations in neutral pH?
Anions are weakly bound to soil particles and can easily be leached out by excess water.
167
Why is it more difficult to acquire cations in acidic soil?
The cations are not bound as well to the clay and so leach out.
168
What is passive transport?
When particles move from high to low concentration. This can either be with simple diffusion or with pumps
169
What is active transport?
This requires energy and moves against the concentration gradient.
170
What is mycorrhizas?
The symbiotic relationship between fungus and root hairs. Plant supplies fungus with carbon and the fungus increases plants nutrients
171
What is nitrogen fixation?
Taking N2 from atmosphere an making NH4+. Done by bacteria
172
What is ammonification?
Breaking decaying organic N into NH4+
173
What is bacterial nitrification?
Bacteria oxidizes NH4+ into NO3- (plants prefer NO3-)
174
What is short distance transport?
Between cells and to and from vascular tissue
175
What is long distance transport?
Movement of substances between root and shoots
176
What is aquaporin?
Proteins that allow rapid movement of water through hydrophobic membrane core
177
In water potential which way does it move?
From high to low water potential
178
How do solutes affect water potential?
It lowers the water potential
179
How does pressure affect water potential?
Positive pressure increases water potential while negative (tension) decreases water potential.
180
What is tonoplast?
the membrane on the vacule
181
What are the three ways solutes travel?
1. Apoplast
2. Symplast
3. Cell to cell
182
What is apoplast
moving between the cells
183
What is symplast?
moving between cells through plasmodesmata
184
How far can solutes move in apoplast?
Only until the reach the casparian strip in the endodermis which then they switch to symplastic
185
What is the casparian strip made of?
suberin which is a waxy substance
186
What are two purposes of the casparian strip?
1. regulates ion and water intake into the plant
| 2. restricts solutes from flowing back
187
What is the greatest loss of water in plants?
Transpiration
188
What is guttation?
when root pressure forces water out of the leaves
189
What is root pressure?
When there is high humidity or low light there is excess water being drawn into the roots and so forces the xylem to move upward. Because this is a slight force it is only effective in small plants.
190
What is translocation?
long distance transport via the phloem
191
Why do substances move in the phloem?
Difference of pressure in the source and sink areas
192
What is the purpose of companion cells?
They acquire sugar from mesophyll then make larger before passing into phloem to prevent back flow. They also support the phloem cell as it no longer has a nucleus
193
What is the stomata made of?
Two guard cells
194
What is the transpiration-photosynthesis compromise?
Stomata open when environmental conditions are favourable
195
What hormone causes the stomata to close?
Abcisic acid (ABA)
196
Where is abcisic acid synthesized?
Roots
197
How does CO2 affect pH?
High CO2 means low pH
| Low CO2 means high pH
198
What the hormones help growth and how do they differ?
Auxins - promote growth
Gibberellins - stimulate growth and elongation of stems
Cytokinins - enhance growth and retard aging
Brassinosteroids - regulate growth
Jasmonates - regulate growth and plant defence
199
What does the hormone ethylene do?
Senescence
200
What does abscisic acid do?
Suppresses growth and responds to environmental stress
201
What hormone is used in herbicide?
Auxins - causes plant to grow too quickly causing it to die
202
How do plants move in response to sunlight?
Auxins cause cells on the far side to elongate cause the stem to bend
203
What is the acid - growth hypothesis?
Auxin moves H+ into the cell wall causing it to have high pH. The cellulose fibers then loosen
204
What does high gibberellin do?
Causes bolting where the plant no longer produces flowers just leaves. Also enlarged fruit
205
What do we mean by perfect flowers?
They are bisexual; having both male and female
206
What do we mean by imperfect flowers?
they only have one sex and so can not self fertilize
207
What does monoecious mean?
The plant has both male and female flowers
| ex Corn
208
What does dioecious mean?
Some plants are all male while other plants are all female
| ex Willow
209
What is double fertilization?
Two sperms are used; one to form the embryo and the other to form the endosperm. Only occurs in angiosperm
210
How do wet and dry stigmas differ?
Dry will only let certain pollen in, wet will let any pollen in but destroy the pollen tube if it is not the correct sperm
211
What is fission reproduction?
Splitting into two individuals of the same size
212
What is budding reproduction?
offspring grows off the parent resulting in two individuals of different sizes
213
What is fragmentation?
When an organism is cut into two pieces and those pieces then grow to become two individuals
214
What is pathenogenesis?
Production of eggs that don't need to be fertilized creating exact clones of the parent
215
When is asexual reproduction favorable?
- unable to find mate
- fast reproduction
- stable environment
216
When is sexual reproduction favorable?
- changing environment (unstable)
| - allows for genetic diversity
217
What is broadcast spawning?
I type of external fertilization where sperm and eggs are released and hoped to be fertilized
218
How can you increase the chances that external fertilization will work?
- mating behaviours
- nest building
- proximity/ timing
219
Why do most land animals have internal fertilization?
Allows them to prevent desication.
220
How do terrestrial animals ensure the right sperm is fertilizing the egg?
Certain behavior patterns or pH level
221
What does the acrosomal reaction do during fertilization?
The acrosome is the head of the sperm. This will make contact with the egg releasing enzymes to dissolve a pathway in the outer layer of the egg. Once the sperm penetrates the vitelline coat with the help of proteins it depolarizes the membrane and fast blocks polyspermy.
222
What does the cortical reaction do during fertilization?
During the fusion of egg and sperm Ca2+ is released starting the cortical reaction where cortical granules coat the egg once again to prevent polyspermy
223
What does oviparous mean?
they lay eggs with shells to keep moisture inside
224
What does viviparous mean?
it is internal growth where the mother provides the nutrients
225
What does ovoviviparous mean?
The egg is developed internally
226
What is direct development?
They young look the same they just need to get larger
227
What is indirect development?
They young look nothing like the adults and usually requires them to pass through stages
228
What does yolk do to an egg?
Yolk is viscous and so prevents cells from dividing and so they become larger than the other ones
229
How do holoblastic and meroblastic eggs differ?
Holoblastic is when there is little yolk and so cells are all the same size.
Meroblastic is when there is lots of yolk and only some cells divide
230
What is the archenteron?
A primitive gut in the early stages of development
231
What does the endoderm form?
gut
liver
lungs
232
What does the ectoderm form?
skin
| nervous system
233
What does the mesoderm from?
muscle
bones
blood
234
What are the homeotic genes?
They regulate the development of the embryo and the fate of the cells
