Question

1) What is endosymbiosis? Which organelles may have arisen this way? What evidence is there for this theory?

2) Which cells in our bodies have cilia and flagella? Can you find other examples? How do these structures differ in structure and movement? How are they similar?

3) How do flagella differ between prokaryotes and eukaryotes?

Answer 1

1. Endosymbiosis , (endo means within, sym means together, bio means living) is a process in which an organism lives within the body or cell of another organism in mutualism.

Endosymbiotic Theory explains origin of organelles in eukaryotic cells by endosymbiosis process.

The most common example of endosymbiosis is Mitochondria in animal cells and Chloroplasts in plant cells.

Mitochondria and chloroplasts are thought to have evolved from bacteria. Both are similar to bacteria in size, and reproduce by dividing into two. They also contain their own DNA and synthesizes their own components. DNA transcribed in the organelles and translated on organelle ribosomes. Thus Mitochondria and chloroplasts contain their own genetic system. Most importantly rRNA of these organelles are closely related to bacterial rRNA.

so the endosymbiotic origin of these organelles is now generally accepted. Mitochondria thought to have evolved from aerobic bacteria and chloroplasts from cyanobacteria.

2. In our body Cilia found in Respiratory tract, Respiratory epithelial cells,Lungs, Fallopian tubes of females, middle ear.

Flagella found in Sperm cells and it helps in movement.

Sperm cell is the only cell in human body which contains flagella.

Cilia  is small slender projections from cell body. present in a large number in a cell. Found only in eukaryotic cells.  

cilia shows rotational motion. They are very fast moving.

Flagella is long , threadlike structure. Less than 10 flagella are present in a cell. Found in both eukaryotic and prokaryotic cells.

Flagella show slow, wave like motion. Sinusoidal and undulating movement.

Structurally Motile cilia and flagella are similar. Both possess 9+2 axoneme arrangement. Non motile cilia possess 9+0 arrangement.

3. Eukaryotic flagella larger and complex structure. Made up of tubulin protein. Needs ATP for movement.

Prokaryotic flagella smaller and simple structure. Made up of flagellin protein. ATP not needed.Proton driven movement occurs.