Unit 9
Diversity of Life Forms
Lecture 2
Recent studies on Archaea suggest that life could have originated (June 2011)
(a) Extra terrestrially and seeded through meteorite impacts.
(b) In shallow coastal areas.
(c) In deep hydrothermal vents.
(d) In hot, terrestrial habitats.
This hypothesis is known as Panspermia. It posits that life exists throughout our
Universe, and it can be spread from planet to planet via space dust, meteorites,
asteroids, and other space objects. Although the idea seems unbelievable, it hasn’t
been ruled out by scientists just yet. Scientists have discovered that extremophiles —
microorganisms that endure extreme conditions — can survive in outer space…
The three-domain classification of life proposed by Carl Woese divides life forms on the
basis of (Nov 2020)
(a)Mitochondrial DNA and membrane structures
(b)Ribosomal rRNA and protein sequences
(c)Mitochondrial DNA and protein sequences
(d)Presence of single or double membranes
Woese used differences in the sequences of nucleotides in ribosomal RNA (rRNA) to differentiate
between domains. Since rRNA molecules perform the same function across species and their structure
changes very little over time, comparing rRNA nucleotide sequences provides insights into the
relatedness of different cells and organisms.
Ans: b
The diagram below depicts a simplified tree of life with three domains and one of the domains
including Whittaker's three major kingdoms. (June 2014)
Which of the following is the correct naming of the
numbered boxes?
a) 1- Bacteria 2 - Archaea 3 – Eukarya 4 - Fungi
b) 1 - Archaea 2 - Bacteria 3 - Eukarya 4 - Plants
c) 1- Eukarya 2 - Bacteria 3 - Archaea 4 - Plants
d) 1- Archaea 2 - Bacteria 3 - Eukarya 4 – Fungi
Given below is a list of bacteria either functioning as methanogens or methanotrophs: (Dec 2018)
A.Methanobacterium sp
B.Methanococcus sp
C.Methylomonas sp
D.Methylosinus sp
Which of the following options classifies the above list correctly?
(a) Methanogen - A; Methanotrophs - B, C, D
(b) Methonogens - A, B, C; Methanotroph -D
(c) Methanogens -A, B; Methanotrophs-C, D
(d) Methonogens - A, D; Methanotrophs -B, C
Ans: c
Identify the proteobacteria based on the key given below: (Dec 2012)
i Cause disease in humans ii
i Do not cause disease in humans iii
(a)A - Rickettsia; B - Brucella; C - Wolbachia; D
ii An obligate intracellular parasite A
Nitrobacter; E - Agrobacterium; F -
ii Not all obligate intracellular B Acetobacter; G- Rhizobium; H – Azospirillum
parasite
iii Live in insects C (b)A - Rickettsia; B - Wolbachia; C - Brucella; D -
iii Do not live in insects iv Nttrobacter; E - Acetobacter; F –
iv Chemoautotrophic D
Agrabacterium; G-Rhizobium; H- Azospirillum
iv Not Chemoautotrophic v (c)A - Rickettsia; B - Brucella; C- Wolbachia;D-
v Plant pathogen E Nitrobacter; E - Agrobacterium;F-Acetobacter;
v Not a plant pathogen vi G- Azospirillum; H- Rhizobium
vi Fix nitrogen vii (d)A- Rickettsia; B - Brucella; C - Wolbachia; D -
vi Do not fix nitrogen F Nilrobacter; E - Acetobacter; F -
vii Associated with legumes G Agrobacterium; G- Azospirillum; H- Rhizobium.
vii Not associated with legumes H
General Biology of the
Protists
The Origin of the Eukaryotic Cell
The modern eukaryotic cell arose in several steps:
• The origin of a flexible cell surface
• The origin of a cytoskeleton
• The origin of a nuclear envelope
• The appearance of digestive vesicles (Lysosomes)
• The endosymbiotic acquisition of certain organelles
THE PROTECTIVE CELL WALL WAS LOST
WHAT A FLEXIBLE CELL SURFACE ALLOWS ??
THE ORIGIN OF A CYTOSKELETON
Cytoskeleton (microfilament
and microtubules) formed.
Internal membranes studded
with ribosomes formed.
THE ORIGIN OF NUCLEUS
As regions of the infolded
cell membrane enclosed
the cell's DNA, a precursor
of a nucleus formed.
Microtubules from the
Early digestive vacuoles cytoskeleton formed
eukaryotic flagellum, enabling
evolved into lysosomes
propulsion.
using enzymes from the
early endoplasmic
reticulum.
THE ORIGIN OF MITOCHONDRIA
Mitochondria formed
through endosymbiosis
with a proteobacterium.
THE ORIGIN OF CHLOROPLAST
Endosymbiosis with
cyanobacteria led to
the development of
chloroplasts.
Studies of plastid-bearing eukaryotes suggest that plastids evolved from a cyanobacterium that was engulfed by
an ancestral heterotrophic eukaryote (primary endosymbiosis).
That ancestor then diversified into red algae and green algae, some of which were subsequently engulfed by other
eukaryotes (secondary endosymbiosis)
Nucleomorphs are small, vestigial eukaryotic nuclei found
Chlorarachiniophyte: A marine between the inner and outer pairs of membranes in
algae certain plastids.
They are thought to be vestiges of primitive red and green algal
nuclei that were engulfed by a larger eukaryote.
Habitat
Most protists are aquatic (marine, fresh water, and some are in the body fluids of other
organisms). The slime molds inhabit damp soil, moist, decaying bark of rotting trees, soil water).
Cell and function
Most protists are unicellular, but some are multicellular.
Metabolic pathways were “borrowed” from bacteria through endosymbiosis.
Nutritional modes in protists
Photosynthetic autotrophs, heterotrophs, between the autotrophic and heterotrophic.
Protists have diverse means of locomotion
Protists locomotion
Amoeboid motion Ciliary motion Flagella motion
The cell forms Cilia are tiny, hairlike A eukaryotic flagellum
pseudopods (“false feet”) organelles that beat in moves like a whip;
that are extensions of its a coordinated fashion
constantly changing to move the cell Some flagella push the
body mass. forward or backward. cell forward, others pull
the cell forward.
Cells such as the amoeba
simply extend a Cilia and eukaryotic
pseudopod and then flow flagella are identical in
into it. cross section; they differ
only in length.
Vesicles perform a variety of functions
How does the contractile vacuole (CV) work?
4
2 3
1 2 3 4
Water passes from the Central vesicles
Expels its content Detachment from the
cytoplasm to radiating canals periodically fuses with the
membrane
and to the central vesicles plasma membrane
Vesicles perform a variety of functions
How does the Food vacuole (FV) work?
Vesicles perform a variety of functions
How does the Food vacuole (FV) work?
Protist Diversity
