Unit 4: Cellular Reproduction

What are some of the difficulties a cellfaces as it increases in size?

1. Larger cells are less efficient in moving nutrients and waste materials across its cell membrane.

The ability of the cell to maintain homeostasis depends on the rapid exchange of materials in the cell.

Analogy

Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are

in greater demand, which limits access.

Application- A growing cell makes greater demands on its genetic “library.”

If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

◦To use the town analogy again, as the town grows, more and more traffic clogs the main street. It becomes difficult to get information across town and goods in and out.

◦Similarly, a cell that continues to grow would experience “traffic” problems. This would inhibit the rapid exchange of material as well and harm the cell

So what is a cell to do in order to get aroundthese problems that result if a cell grows too large?

◦Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.

◦Before cell division, the cell copies all of its DNA.

◦ It then divides into two “daughter” cells. Each daughter cell receives a complete set of DNA.

In multicellular organisms, cell division leads togrowth.

◦It also enables an organism to repair and maintain its body.

◦In some organisms, cell division is a form of reproduction called ASEXUAL REPRODUCTION .

1) Asexual Reproduction

2) Sexual Reproduction

Description- reproduction that involves a single parentproducing an offspring which is genetically identical to the‘parent’ that produced them.

Benefits of this mode of reproduction- ◦ It is a simple, efficient, and effective way for an organism

to produce a large number of offspring.

Who uses this method of reproduction?

◦Both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually.

Bacteria reproduce by binary fission.

Kalanchoe plants form plantlets.

Hydras reproduce by budding.

Description - Mode of reproduction which involves thefusion of two sex cells (ex: sperm & egg) – one from eachof two parents; which results in the creation of geneticallyunique offspring.

◦ The sex cells fuse into a single cell before the offspring can grow.

What are the benefits of this mode of reproduction?

◦Offspring are GENETICALLY UNIQUE because they inherited some genetic information from both parents.

◦ This genetic diversity helps to ensure the survival of the species when the environment changes

Who uses this mode of reproduction?

◦Most animals and plants, and many single-celled organisms, reproduce sexually.