Chapter 9.4

Cytoplasmic Division Mechanisms

AP BiologyFall 2010

Objectives

• Describe the differences of the cytoplasmic division mechanisms in animal and plant cells

How Do Animal Cells Divide?

• Cytokinesis: cytoplasmic division in animals by means of a cleavage furrow

How Do Animal Cells Divide?

• Contractile ring mechanism• Flexible plasma membrane of animal cells can

be squeezed in the middle to separate two daughter cells

• Cell cortex, mesh of cytoskeletal elements under plasma membrane, is a ring of actin filaments organized as a thin band around cells midsection

How Do Animal Cells Divide?

• Band anchored to plasma membrane• Parallel arrays of contractile microfilaments

slide past one another when activated by ATP at the cleavage furrow, pulling the plasma membrane inward

• Each daughter cell ends up with a nucleus, some cytoplasm (with organelles), and a plasma membrane

How Do Plant Cells Divide?

• Because of ridged cell wall, cytoplasm of plant cells cannot just be pinched in two

• Vesicles produced by Golgi containing remnants of the microtubular spindle form a disk-like structure between the two new cells – Called cell plate

How Do Plant Cells Divide?

• Microtubules beneath plasma membrane help orient the fibers of cellulose in the wall

• Wall grows until it bridges the cytoplasm and partitions the parent cell

• Cytoplasmic division mechanisms known as cell plate formation

How Do Plant Cells Divide?

Appreciate the Process!

• Failure of chromosomes to duplicate precisely or distribute properly can result in genetic disorders and cancer

• This failure may start in body cells and in germ cells

Review

1. What mechanism do animal cells use for cytoplasmic division?

2. What mechanism do plant cells use for cytoplasmic division?

Answers

1. Animal cells use the contractile ring mechanism and a cleavage furrow.

2. Plant cells use cell plate formation.