Download Chapter 8: Cell Reproduction

Cell Reproduction Unit
Part 1:
Overview
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
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
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.
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
Cell Division & Reproduction
• All organisms produce new organisms
like themselves
• During reproduction, organisms transmit
hereditary information
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.
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
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”?
Facts about DNA
• It is a long, thin molecule that stores ________
______________.
• It is made of nucleotides
• Nucleotides are made of:
a sugar, a phosphate, and a nitrogen
base
• In human cells, its consists of approx. 3 billion
nucleotides
• In eukaryotes, DNA is found in the _________.
• In prokaryotes, DNA is found in the
___________.
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
Chromosome Structure of
Eukaryotes
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Chromosome Structure
• Each chromosome
consists of 2
identical halves
called
___________
• The 2 chromatids
are held together
by a
______________.
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
Chromosome Number
• Every species has a
characteristic number of
chromosomes in each cell
• Human & animal
chromosomes are
categorized into 2
groups: ____________
& _______________.
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)
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
Human Karyotype
• A karyotype is
pictorial
diagram
showing all the
chromosomes
of an organism
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 = ____