Lecture 1

Question 1

What are the three major steps in the development of life towards animals?

Answer 1

Life originated about 4 billlion years ago (believed to be similar to prokaryotes)

2. 1 Billion years ago the eukaryotes formed
3. 5 billion years ago multicellular life began

Question 2

What is the hadean era?

Answer 2

The era just after earth was formed 4.5 to 3.9 billion years ago when the environment was too harsh due to high temperatures and levels of volcanic and meteoric activity for life to form

Question 3

What is the first evidence of life?

Answer 3

There is chemical evidence of life in 3.8 billion year old rocks in Issua, Greenland from an abundance of carbon isotopes which MAY be due to life
There is what is suspected to be the oldest fossil from 3.5 billion years ago seen in Western Australia which resembles some modern prokaryotes

Question 4

How are prokaryotic organisms metabolically diverse?

Answer 4

There are autotrophs which can photosynthesize sugars, chemoautotrophs which produce energy from inorganic chemicals and heterotrophs which gain energy from organic chemicals synthesized by other animals

Question 5

What are the two forms of membranes which can be seen in prokaryotes?

Answer 5

Respiratory membranes in oxygen breathing (aerobic forms) and thylakoid membranes in photosynthetic memebranes

Question 6

What is the oldest evidence of eukaryotes?

Answer 6

The oldest definite fossil is 2.1 billion years old but some possible chemical fossils have been dated to 2.2 billion years ago with the earliest chemical evidence being 2.7 billion years ago

Question 7

What are the two major stages in the evolution of eukaryotes/

Answer 7

There was an increase in size and compartmentalization

This was followed by symbiogenesis which occured at least twice to establish the mitochobdria and chloroplast

Question 8

What is the evidence for the symbiogenesis generating the mitochondria?

Answer 8

there is similarity between respiratory membranes in oxygen breathing prokaryotes and mitochondria and thylakoid membranes and chloroplasts
both organelles also have there own DNA which is structured like prokaryotic DNA

Question 9

What is the first division among the invertebrates?

Answer 9

The metazoa breaks into the Parazoa and Eumetazoa, with Parazoa believed to be the oldest living animals, lacking true tissues and containing only porifera (sponges) as a living phyla

Question 10

What are the features of the porifera phyla?

Answer 10

About 9100 species and originated at least 700 million years ago
Believed to have evolved from unicellular choanoflagellates as some sponge cells are almost identical

Question 11

What are the features of choanoflagellates?

Answer 11

They are tiny, single celled protists with a characteristic collar and flagellum and typically live in colonies

Question 12

How did sponge ancestors evolve from unicellular protists?

Answer 12

1. There was a colonial protist aggregate of identical cells
2. There was a hollow sphere of unspecialized cells
3. There was the beginning of cell specialization with repoductive cells forming
4. There was a slight infolding in the ball of cells
5. There was gastrula like infolding forming a proto-animal with a digestive cavity

Question 13

What are the common features of sponge ecology?

Answer 13

They are sessile or fixed in one place
All are aquatic and mostly marine (9000 marine, 100 freshwater)
They are filter feeders which use water currents to trap bacteria and small organic material from which it derives its energy
Although one species Cladorhizidae, is known to be carnivorous

Question 14

What is the form of sponges (porifera)?

Answer 14

Have a large external size range (2m to 1cm)
resembles a sac perforated with pores (ostia) through which water flows, the body wall filters out food particles and residual water then passes into the spongocoel and returned to the environment through the osculum

Question 15

What are the layers seen in sponges (porifera)?

Answer 15

Pinacoderm which is the outer layer in contact with the environment and consists of a single layer of pinacocytes which may be modified to form porocytes which from the ostia
Mesohyl whichis the middle layer which is not a continuous layer of cells but rather a gelatinous matrix containing mobile amoebocytes which have several functions including nutrient transport, gamete formation, secretion of the skeleton (made of spongin)
Choanoderm which is the innermost layer lining the spongocoel made of a single layer of choanocytes which in some species form the gemetes though their main function is feeding with a flagellum which beatd to create a flow of water and a mucus collar to trap food particles which will be taken up into vacuoles and passed on to amoebocytes