1. Cell Reproduction Unit
Part 1:
Overview

2. Objectives
Be able to explain the difficulties a cell faces as it increases in size
Be able to compare and contrast sexual & asexual reproduction
Be able to describe the structure of a chromosome
Be able to identify the differences in structure between prokaryotic chromosomes and eukaryotic chromosomes
Be able to explain the differences between sex chromosomes and autosomes

3. Limits to Cell Size Nearly all cells grow by increasing in size
At some point, they divide
There are two main reasons cells divide rather than continue growing:
Information Overload
The larger a cell becomes, the more demands the cell places on its DNA
Exchanging Materials
A larger cell is less efficient in moving nutrients and waste materials across the cell membrane

4. Surface Area to Volume Ratio
The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or its surface area–to–volume ratio
As a cell grows, its volume increases much faster than its surface area does
Why is this important to cells?
This trend is important because the materials needed by a cell, such as nutrients and oxygen and the wastes produced by a cell, such as carbon dioxide must pass into and out of the cell through its surface.

5. Division of the Cell
Before a cell becomes too large it divides into two “daughter” cells
Cell Division: is the process by which a cell divides into two new daughter cells

6. Cell Division & Reproduction
All organisms produce new organisms like themselves
During reproduction, organisms transmit hereditary information

7. Two Types of Reproduction
Asexual Reproduction: produces new organisms that are exactly the same as the original organism
Examples: strawberries, amoebas, bacteria, starfish, onions etc.
Sexual Reproduction: produces a genetically unique organism from the combining of the parents’ DNA
Examples: humans, tigers, some plants, whales, etc.

8. Compare & Contrast Asexual Reproduction Sexual Reproduction
Needed for the survival of a species
Happens faster
Offspring are exact copies of parents
Lack of genetic diversity
Needed for the survival of a species
Takes longer
Offspring are a combination of parents DNA
Lots of genetic diversity

9. Visual Analogy Activity
In the assigned groups, discuss the following and be prepared to share with the class.
How could cell growth create a problem that is similar to a traffic jam?
How does a cell solve the “traffic jam” like a growing city would?
Why are cells concerned with “traffic jams”?

10. Facts about DNA
It is a long, thin molecule that stores ________ ______________.
It is made of nucleotides
Nucleotides are made of:
In human cells, its consists of approx. 3 billion nucleotides
In eukaryotes, DNA is found in the _________.
In prokaryotes, DNA is found in the ___________.
a sugar, a phosphate, and a nitrogen base

11. Chromosomes
Chromosomes are rod-shaped structures made of DNA & proteins
The DNA & proteins are tightly coiled together
The proteins that eukaryotic DNA wraps around are called histones
Histones help maintain the shape of a chromosome & keep it tightly packed

12. Chromosome Structure of Eukaryotes
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones

13. Chromosome Structure
Each chromosome consists of 2 identical halves called ___________
The 2 chromatids are held together by a ______________.

14. Chromosome Structure
Normally DNA is not so tightly coiled into chromosomes
Chromosomes only appear right before cell division
When cell division is not occurring, DNA is less tightly coiled as __________.
Why is the DNA not kept tightly packed all the time?
Because it is easier to copy (transcribe) in its chromatin form, which happens before division occurs

15. Chromosome Number
Every species has a characteristic number of chromosomes in each cell
Human & animal chromosomes are categorized into 2 groups: ____________
& _______________.

16. Sex Chromosomes & Autosomes
Sex chromosomes: are the chromosomes that determine the sex of an organism
In humans, they are either X or Y
Females are XX
Males are XY
Autosomes: are all the other chromosomes of an organism
Humans have 44 autosomes (22 pairs)

17. Chromosome Numbers
Every organism produced by sexual reproduction has 2 copies of each autosome
One copy comes from _____ and the other comes from ______.
The 2 copies of each autosome are called homologous chromosomes
Meaning they are the same size, shape and carry the same traits

18. Human Karyotype
A karyotype is pictorial diagram showing all the chromosomes of an organism

19. Chromosome Numbers: Diploid vs. Haploid Cells
Diploid cells: have 2 sets of homologous chromosomes
All human cell except the sex cells are diploid
Abbreviated 2n
In humans, 2n = ____ or ____ pairs
Haploid cells: have only 1 set of chromosomes
Sperm & egg cells are haploid
Abbreviated 1n
In humans, 1n = ____