CELL REPRODUCTION • at This Very Moment, Cells All Over Your Body Are Growing and Dividing

Pre-Discussion Thinking Questions:

•To be considered LIVING or ALIVE, organisms must be able to REPRODUCE. What does this mean?

•Why is it important for an organism to be able to reproduce? • What must happen in order for reproduction to occur?

• You need… DNA • Genetic material found in the nucleus of all cells. DNA is your genetic blueprint (instructions) for all your cell’s activities and all the characteristics of an organism. DNA • DNA stands for DEOXYRIBONUCLEIC ACID • DNA has specific segments, called GENES. Each gene controls one particular trait, although sometimes more than one gene can control one trait. DNA • DNA is shaped like a twisted ladder (also called a double helix). It has sides (like the handrails of a ladder) and rungs (called bases). The bases are what provide a code. The code tells your cells and whole body what to do. Chromosomes • Made of long strands of DNA • You have 46 chromosomes in your cells (23 PAIRS.) One SET came from “MOM” and one from “DAD”. The pairs are held together by a CENTROMERE. Chromosomes

• Play an important part in cell division; • Also called CHROMATIN CELL REPRODUCTION • At this very moment, cells all over your body are growing and dividing. How does this happen? • Just as organisms go through stages, or a life cycle, so do CELLS. • Most of a cell’s life is spent in a period of growth & development called INTERPHASE • During this time, the cell is NOT dividing.

Cells that no longer DIVIDE are always in interphase.

Examples include NERVE CELLS, BRAIN CELLS.

• Cells that actively divide—such as SKIN cells— have a more complex cell cycle.

• The process through which cells divide is called MITOSIS MITOSIS (My-toe-sis) • Also known as regular cell division. • Two cells are created from one • Each new cell has a nucleus that contains the same number and type of CHROMOSOMES as the original cell MITOSIS (My-toe-sis) Important to Remember! • Human cells have 46 chromosomes in their nuclei, so after cell division, each new nucleus will have 46 chromosomes—not 23, because the chromosomes duplicate themselves before the cell divides. • (So at one point during cell division, your cells actually have 92 chromosomes!) Plant Cell Mitosis —same process with a few twists! • Because plant cells have rigid WALL, they do not PINCH IN like animal cells do. • Instead, they form a structure called a CELL PLATE , where a new CELL WALL will form ASEXUAL REPRODUCTION • Reproduction by one parent organism • Offspring that are produced by asexual reproduction have DNA that is IDENTICAL to that of its one parent. ASEXUAL REPRODUCTION • Regular cell division is considered asexual reproduction. • Some organisms use asexual reproduction to create whole new organisms from just one parent. Types of Asexual Reproduction Budding • Budding is a type of asexual reproduction where the new organism GROWS FROM THE BODY of the parent and when it becomes large enough, it BREAKS OFF & lives BY ITSELF.

• Examples include: YEAST, HYDRA, AND SPIDER PLANTS, Budding Spider plants Hydra

Strawberries Potatoes Types of Asexual Reproduction Regeneration • During regeneration, a whole organism may develop from just a PART of the organism. • Or you can get 2 ORGANISMS when there is injury to ONE. • Examples include: SEA STARS, SEA SPONGES, PLANARIA Regeneration Types of Asexual Reproduction

Fission • This process divides them into two EQUAL PARTS. (just like splitting something in half evenly)

• Bacteria are organisms that divide by fission

Asexual Reproduction Clip Cloning • Cloning is asexual reproduction, because there is only one parent providing DNA for the new organism, which would make the offspring genetically identical to its one parent.

• Not a new process—people have been performing it for thousands of years on plants! Cloning • Scientists have cloned a few animals, like Dolly the sheep in 1997 Cancer • When cells don’t STOP dividing the way they are supposed to • Results in the growth of a tumor (mass of cells) • Some tumors are benign (harmless) and some are considered dangerous (when they don’t stop growing, they can spread to other parts of the body) Cancer How is this different from asexual reproduction??? Sexual Reproduction • New organism is produced when sex cells from two different parents join together. • Offspring that are produced by sexual reproduction have DNA that is DIFFERENT compared to both of its parents. Sexual Reproduction

• Most plants and animals reproduce in this manner. • Remember what we call the reproductive part of a plant? Flowers! • Males make one kind of sex cell, called the sperm. EGG • These are produced by the testes.

SPERM • Females make one kind of sex cell, called the egg. • These are produced by the ovaries. • Sex cells are usually different in size. • Sperm are small, with all of the genetic material crammed into the “head”. • Eggs are large. • Why might this be so?

• Once two sex cells have joined, we say that fertilization has occurred. • The new cell that forms is called a zygote. • If you have an egg cell with 10 chromosomes joining a sperm cell with 10 chromosomes, how many chromosomes will the new baby cell (the zygote have)? • 20 • A human body cell has 23 pairs of chromosomes • A human sex cell has only 23 individual chromosomes.