Cellular Division & Cellular Division & ReproductionReproduction

Why is cell division Why is cell division important?important?

Your body is made up of cells- Your body is made up of cells- trillions trillions of cells.of cells.

Many organisms start as just Many organisms start as just one one cell. That cell divides and cell. That cell divides and becomes becomes two, two two, two becomes becomes four, four, four becomes four becomes eight, eight, and so on. and so on.

Many-celled organisms, including Many-celled organisms, including you, grow because you, grow because cell division cell division increases the total number of increases the total number of cells in an cells in an organism. organism. Even after Even after growth stops, cell division is growth stops, cell division is still still important.important.

Every day, billions of red blood cells Every day, billions of red blood cells in your body wear out and are in your body wear out and are replaced. During the few seconds it replaced. During the few seconds it takes you to read this sentence, takes you to read this sentence, your your bone marrow bone marrow produces about produces about six million six million red red blood cells. Cell blood cells. Cell division isn’t as simple as just division isn’t as simple as just cutting the cell in cutting the cell in half, half, so how do so how do cells divide?cells divide?

Red blood cells shown Red blood cells shown from a SEMfrom a SEM

The Cell CycleThe Cell Cycle

A living organism has a life cycle. A A living organism has a life cycle. A life cycle begins with the life cycle begins with the organisms formationorganisms formation followed by followed by growth growth and and development, development, and and finally ending in death.finally ending in death.

Right now you are in the stage of Right now you are in the stage of your life called your life called adolescence, adolescence, which is a period of active growth which is a period of active growth and development.and development.

Length of CycleLength of Cycle

The cell cycle is a series of events The cell cycle is a series of events that takes place from one cell that takes place from one cell division to the next. The time it division to the next. The time it takes to complete the cell cycle is takes to complete the cell cycle is NOT NOT the same in all cells.the same in all cells.

In some human cells, the cell cycle In some human cells, the cell cycle takes about takes about 16 hours.16 hours.

Types of ReproductionTypes of Reproduction

Reproduction is the process by Reproduction is the process by which an organism which an organism produces produces others of its same kind. others of its same kind. Among Among living organisms, there are two living organisms, there are two types of reproduction- types of reproduction- sexual sexual and and asexual.asexual.

Sexual reproduction usually Sexual reproduction usually requires requires two two organisms. organisms.

In In asexual asexual reproduction, a new reproduction, a new organism is produced from organism is produced from one one organism. organism.

The new organism will have The new organism will have hereditary material of the hereditary material of the parent parent organism.organism.

Asexual ReproductionAsexual Reproduction

Organisms with Organisms with eukaryotic eukaryotic cells cells asexually reproduce by asexually reproduce by mitosis mitosis and and cell division. cell division. New strawberry New strawberry plants can be reproduced plants can be reproduced asexually asexually from horizontal stems from horizontal stems called runners. called runners.

Bacteria can reproduce asexually Bacteria can reproduce asexually by the process called by the process called fission. fission.

During fission, the one-celled During fission, the one-celled bacterium without a nucleus bacterium without a nucleus copies its copies its genetic material genetic material and and then divides into then divides into two two identical identical cells.cells.

Potatoes reproduce by budding. Potatoes reproduce by budding. Budding is a type of Budding is a type of asexual asexual reproduction made possible reproduction made possible because of mitosis and because of mitosis and cell cell division. division. When the bud becomes When the bud becomes large enough, it breaks away to large enough, it breaks away to live on its own.live on its own.

Potatoes BuddingPotatoes Budding

Budding HydraBudding Hydra

Some organisms can regrow Some organisms can regrow damaged or damaged or lost lost body parts. body parts. Regeneration Regeneration is the process that is the process that uses mitosis and cell division to uses mitosis and cell division to regrow body parts. regrow body parts.

Sponges, planaria, and Sponges, planaria, and sea stars sea stars use regeneration.use regeneration.

Budding of sea starBudding of sea star

Cloning is another type of Cloning is another type of asexual asexual reproduction. reproduction.

Cloning Cloning describes a process that describes a process that can be used to produce can be used to produce genetically genetically identical copies of a identical copies of a biological entity.biological entity.

The copied material which has the The copied material which has the same genetic makeup of the same genetic makeup of the original, is referred to as a original, is referred to as a clone.clone.

Dolly (first cloned Dolly (first cloned sheep)sheep)

Sexual ReproductionSexual Reproduction

During sexual reproduction, During sexual reproduction, two two sex cells, sometimes called an sex cells, sometimes called an egg and sperm, come together.egg and sperm, come together.

Sperm are formed in Sperm are formed in male male reproductive organs, and eggs reproductive organs, and eggs are formed in are formed in female female reproductive reproductive organs.organs.

The joining of an egg and sperm is The joining of an egg and sperm is called called fertilization, fertilization, and the cell and the cell that forms is called a zygote.that forms is called a zygote.

Following fertilization, mitosis and Following fertilization, mitosis and cell division begin. A new cell division begin. A new organism with a unique organism with a unique identity identity develops.develops.

Your body forms two types of cells- Your body forms two types of cells- body body cells and cells and sex sex cells.cells.

Body cells far outnumber sex cells. A Body cells far outnumber sex cells. A typical human body has 46 typical human body has 46 chromosomes. chromosomes. Human Human body cells have body cells have 23 23 pairs of chromosomes.pairs of chromosomes.

When cells have similar pairs of When cells have similar pairs of chromosomes, they are said to be chromosomes, they are said to be diploid.diploid.

Sex cells Sex cells do not do not have pairs of have pairs of chromosomes, they are called chromosomes, they are called haploid.haploid.

They have only half the number of They have only half the number of chromosomes as body cells. Haploid chromosomes as body cells. Haploid means means “single form”.“single form”.

Human sex cells have only Human sex cells have only 23 23 chromosomes- one from each of the chromosomes- one from each of the 23 pairs of similar chromosomes.23 pairs of similar chromosomes.