BIOL3711 Lecture Notes - Lecture 3: Sexual Reproduction, Gymnodinium, Oogamy
26 Jun 2018
School
Department
Course
Professor
Green Algae
General
Grow on the surface of stagnant water and damp areas
Chloroplasts are masked by different pigments
Diversity:
oMost diverse group of algae – in structure and life
oAbout 7000 species
Habitats:
oGenerally found in water but grow on:
Snow surface
Tree trunks
Soil
Symbiotic relationships with lichen, protozoans and hydras
Characteristics
Body forms:
oUnicellular
oColonial
oFilamentous
Chloroplast
oOrganelle containing chlorophylls and other pigments
Chlorophyll a, b, B-carotene
Function
oPhotosynthesis
Shape
oCup, star, net, spiral, bar
Cell wall
o2 layers
oInside:
Cellulose
oOutside
Pectin (carbohydrate)
Pyrenoid
oA structure on the chloroplast to produce starch
Food reserve
oStarch
Stigma/eyespot
oRed spot close to flagella
oFunction: light perception
oPhototaxis: algae move towards or against light source
Positive phototaxis – toward light
Negative phototaxis – away from light
Flagella
oNone
o2 or more – equal length
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Classification
Kingdom: PROTISTA
oPhylum: CHLOROPHYTA
oClass
Chlorophyceae
Ulvophyceae
Zygenmatophyceae
Class: CHLOROPHYCEAE
Most green algae
1. Motile unicellular form
Representative genus: Chlamydomonas
Body
oGreen, rounded or pear shaped
o2 flagella
o1 eyespot
oPyrenoid: roughly spherical
oTwo contractile vacuoles: collect
excessive water and discharge it from
cell
Reproduction
Asexual
oLose flagella and form a wall
o4 daughter cells are formed
oIf condition is favourable:
4 daughter cells will be released
oIn absence of water:
Gelatinous sheath forms
oCells develop flagella when flooded
Sexual
oIsogamy
Formation of gametes (isogamete)
Pairing up compatible gametes
Fusion
Zygote: one zygote has 4 flagella (2n)
Dormant zygote with a thickened wall
Meiosis occurs
Release daughter cells (1n) after a period of dormancy
ONLY the ZYGOTE is DIPLOID
Every other cell in life is haploid
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2. Motile colonial form
Many Clamydomonas-like cells adhere in a colony that is propelled by the
beating of flagella of individual cells
1. Gonium (genus)
a. Simplest member
b. Cells held together within gelatinous matric
c. Cells are similar in size
d. Flagella of each cell beat separately, pulling
entire colony forward
e. Each colony is made up of 4, 8, 16 or 32 cells
f. Sexual reproduction
f.i. Isogamy (sperm and egg same size with flagellum
2. Eudorina (genus)
a. Spherical colony is made up of many flagellates
b. Number of cells: 8, 16, 32, 64 or 128
c. Some cells are SMALLER than others
c.i. But smaller cells are incapable of
reproducing new colony
d. Sexual reproduction: oogamy (large egg with no
flagellum and small sperm)
3. Volvox (genus)
a. Many flagellated cells form a hollow sphere
b. Single layer of many biflagellated cells
c. Cells are different size
c.i. Some are vegetative
c.ii. Some are reproductive
d. Carries daughter colony inside the mother colony
e. Sexual reproduction: oogamy (large egg with no flagellum and small
sperm)
3. Non-motile unicellular form
Representative: Chlorella
oNo flagella
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Document Summary
Grow on the surface of stagnant water and damp areas. Diversity: most diverse group of algae in structure and life, about 7000 species. Habitats: generally found in water but grow on: Symbiotic relationships with lichen, protozoans and hydras. Chloroplast: organelle containing chlorophylls and other pigments. Shape: cup, star, net, spiral, bar. Pyrenoid: a structure on the chloroplast to produce starch. Stigma/eyespot: red spot close to flagella, function: light perception, phototaxis: algae move towards or against light source. Flagella: none, 2 or more equal length. Most green algae: motile unicellular form. Body: green, rounded or pear shaped, 2 flagella, 1 eyespot, pyrenoid: roughly spherical, two contractile vacuoles: collect excessive water and discharge it from cell. Asexual: lose flagella and form a wall, 4 daughter cells are formed, if condition is favourable: 4 daughter cells will be released: in absence of water: Gelatinous sheath forms: cells develop flagella when flooded. Zygote: one zygote has 4 flagella (2n)
