Download Biology Unit - Cell Growth and Reproduction The Cell Theory The

Biology Unit - Cell Growth and Reproduction
What makes a plant cell different from an animal cell?
The Cell Theory
Cell wall is a fibrous wall that provides structure and support for the
plant cell. The cell wall is made up of a material called cellulose.
The cell theory states:
All living organisms are made up of one or more cells.
Cells are the basic units in all living organisms.
All cells come from other cells.
The activity of an entire organism depends on the cells.
Chloroplasts is the organelle that allow plant cells to make their own
food through the process of photosynthesis.
The Parts of the Animal and Plant Cells
DNA: The Genetic Material
Plant and animal cells have many membrane bound organelles that
help cells to perform all of their necessary jobs.
All living organisms have a specific number of chromosomes found in
each of their cells. These chromosomes are made up of a chemical
known as deoxyribonucleic acid or DNA
The nucleus acts as the control center for the cell. It coordinates,
controls and manages cell functions.
What does DNA do?
Chromosomes are thread-like structures that carry genetic
information. Chromosomes are found in the nucleus of every cell.
Genes are units of genetic information that determine the specific
characteristics of an individual.
• DNA gives directions to your cells to either repair damaged cell parts
or to make new cells.
• DNA tells the cell how to respond to changes in their environment and
how to respond to messages sent by other cells.
The nucleolus is the darker area found inside the nucleus.
What does DNA look like?
Ribosomes build proteins that are necessary for cell growth and
reproduction.
•
DNA molecules are shaped like a twisted ladder.
The cell membrane acts like the gatekeeper; it controls the movement
of materials in and out of the cell.
•
Sugars and phosphates molecules make up the
sides of the ladder to give DNA its shape.
The cytoplasm is a jelly-like material that supports the nucleus and
the other organelles. Also, nutrients are absorbed, transported and
processed in the cytoplasm.
•
The rungs of the ladder are made up of nitrogen
bases.
•
The order in which the nitrogen bases are placed in
the strands of DNA, is known as the genetic code.
•
The genetic code is arranged in 3 character
sequences of nitrogen bases.
•
These 3 character sequences tell information about
an individual’s genes (eye colour, hair colour, artistic
ability, etc…).
The endoplasmic reticulum is a series of canals that transports
materials to different parts of the cell.
Mitochondria provides the cell with energy.
Golgi bodies store proteins until they are needed by the cell.
Lysosomes are saclike structures that contain proteins that break
down food and digest wastes and worn-out cell parts.
Centriole is a small protein structure critical for cell division.
Vacuoles are fluid-filled storehouses that contain water, food, wastes
and other materials.
Nitrogen Bases Combination
Three types of known carcinogen:
Adenine always pairs with thymine
• Viruses – some cause leukemia
• Radiation – ultraviolet radiation from the Sun
• Hazardous chemicals – Cigarette Smoke
A
T
The Cell Cycle
Cytosine always pairs with Guanine
C
G
DNA Replication
How does DNA make a copy of itself?
1. The two strands of DNA “unzip”.
2. Each strand serves as an outline for a new and complementary
strand to be built.
3. The complementary DNA strand is built when spare nitrogen bases
attach to the original strand of DNA.
• All of the cells in your body divide to make more cells. Most cells in
your body divide by way of mitosis. However, your sex cells are an
exception to this rule; they divide by way of meiosis.
• The cell cycle is the sequence of events that occurs from one cell
division to the next cell division. Cell division is only a small phase
in the entire process of the cell cycle.
The Importance of Cell Division
• Cell division is when one cell divides into two identical cells. Cell
division occurs for three main reasons:
• Healing and Tissue Repair
• Growth
• Reproduction
The Cell Cycle
• All of the cells in your body divide to make more cells. Most cells in
your body divide by way of mitosis. However, your sex cells are an
exception to this rule; they divide by way of meiosis.
Changes to the DNA
• The cell cycle is the sequence of events that occurs from one cell
division to the next cell division. Cell division is only a small phase
in the entire process of the cell cycle.
• Mutations are changes that occur to the genetic code (DNA). Some
of these changes can happen when DNA is exposed to certain
chemicals.
• Some mutations can be beneficial to the DNA but most mutations
are either neutral or damaging to the DNA.
• Mitosis involves four major phases that always take place in the
same order: prophase, metaphase, anaphase and telophase.
CANCER: A deadly mutation
Phase 1: Prophase
• Cancer occurs when cell division goes out of control.
• All cancers are caused by mutations in the genes that control cell
division.
• A carcinogen is any substance or energy that causes such a
mutation.
• During this phase the nucleolus and the nuclear membrane
disappear. The spindle fibers appear and move to opposite ends
of the cell. The spindle fibers then attach to the chromosomes.
The Phases of Mitosis
Cytokinesis
• Cell division continues with the separation of the cytoplasm and its
organelles into two equal parts. This process is called cytokinesis.
This process begins before mitosis is complete.
Phase 2: Metaphase
Interphase
• In metaphase, the spindle fibers pull the double-stranded
chromosomes into a line across the middle of the cell.
• Mitosis and cell division take up only a small fraction of the cell’s life.
Interphase is the stage at which the cell spends most of its time.
During interphase, the cells grow, replicate their DNA, and prepare
for the first phase of mitosis.
Phase 3: Anaphase
• In anaphase, the spindle fibers begin to contract and shorten. This
action pulls the chromosomes apart. The single strands of
chromatin start to move toward the opposite ends (poles) of the cell.
Phase 4: Telophase
• One complete set of chromatin is now at each pole of the cell. The
spindle fibers begin to disappear and a nuclear membrane forms
around each set of chromosomes. The cell in now starting to split
into 2 cells.
Formation of Sex Cells
• Sex cells are formed during the process of meiosis. This process
makes sure that sex cells contain only one-half set of chromosomes
compared to other cells. Meiosis also makes sure that each sex cell
has a different combination of the chromosomes.
Anaphase I - Spindle fibres pull the homologous pairs of
chromosomes apart and pulls the chromosomes to separate ends of
the cell.
Telophase I - A nuclear membrane form around each group of
chromosomes and the cytoplasm splits in half to form two new cells (in
humans there are 23 chromosomes in each new cell).
Example: A human cell containing 46 chromosomes undergoes
meiosis to produce sex cells that have 23 chromosomes.
• When a cell contains the full number of chromosomes, it is referred
to as the diploid chromosome number (2n).
• The haploid chromosome number (n) is when a cell’s chromosome
number is halved.
Example: In humans -- Diploid # = 46
Haploid # = 23
Variance and Homologous Pairs
• Organisms that reproduce sexually show greater variance than
those that reproduce asexually.
• Variance means differences in characteristics.
• An offspring receives a set to 23 chromosomes from each parent.
• The chromosomes that are similar in shape, size and gene
arrangement are combined and these are called homologous pairs
of chromosomes.
Meiosis II
Prophase II -The nuclear membrane dissolves, and spindle fibres start
to grow.
Metaphase II -Spindle fibres attach to the chromosomes (23 in
humans) and pull them in a straight line across the cell.
Anaphase II - The spindle fibres pull on the chromosomes and they
break into chromatin. The sets of chromatin move to opposite ends of
the cell.
Telophase II - A nuclear membrane forms around each set of
chromatin (in humans -23 chromatin in each set) and the cytoplasm
divides. By this stage there are 4 new cells made that have 23 strands
of chromatin in each cell.
• The appearance of the organism is determined by the way the
genes from this pair interact. (colour of hair, eyes, etc…)
Meiosis: The process that involves two cell divisions to produces 4
haploid cells .
Meiosis I
Prophase I - The nuclear membrane dissolves, spindle fibres start to
grow and chromosomes pair up with their homologous pair.
Metaphase I - Spindle fibres attach to the pairs of chromosomes and
these pairs line up.
Interphase - Each of these new cells go through interphase. They
grow to full size and each strand of chromatin makes a copy of itself.
Now each of the cells has a haploid number of chromosomes.
Asexual Reproduction
Asexual reproduction is when an organism produces offspring
without the help of another individual. These offspring have identical
genetic information as the parent.
Examples: some plants, single celled organisms, human somatic cells
Sexual Reproduction
Sexual reproduction the genetic information from two individuals
combines to produce a new and unique individual.
Examples: some plants, most animals, some insects
Types of Asexual Reproduction
There are 5 known ways in which organisms can reproduce asexually;
Atypical Meiosis
• During meiosis there is a possibility of a mistake to occur, this
mistake is known as nondisjunction.
• Nondisjunction is when the two homologous pairs of chromosomes
move to the same pole during Anaphase I. This mistake causes one
of the daughter cells to be missing a chromosome while the other
daughter cell will have one too many chromosomes.
• Examples: Down Syndrome, Turners Syndrome, Klinefelters
Syndrome, etc…
The Importance of Cell Division
Cell division is when one cell divides into two identical cells. Cell
division occurs for three main reasons:
– Healing and Tissue Repair
– Growth
– Reproduction
Reproduction and Cell Division
All organisms reproduce in at least one of two ways;
1) Asexual Reproduction
2) Sexual Reproduction
Some organisms may be able to reproduce by both ways. Examples:
trees and bacteria
1) Binary Fission
2) Budding
3) Fragmentation
4) Spore Formation
5) Vegetative Reproduction
Binary fission is when an organism splits directly into two equal-sized
offspring, each with an exact copy of the parent’s genetic information.
Example: Bacteria
Budding is when the offspring begins as a small outgrowth from the
side of the parent and eventually it breaks off and is able to live as an
organism on its own. Example: Hydra
Fragmentation is when a new organism is formed from a part that
breaks off from the parent.
Examples: worms, algae, star fish, and some plants
Spore formation is when organisms undergo frequent cell divisions to
produce smaller identical spores. Example: Mold
Vegetative reproduction is when some plants produce runners that
eventually develop into other plants.
Examples: Strawberries and Spider Plants
Sexual Reproduction
Sexual reproduction produces unique or non-identical individuals. In
order to produce these unique individuals, the body has specialized
organs that make sex cells (sperm cells and egg cells).
Pollination
In sexual reproduction, the sex cells from two parents combine during
a process called fertilization. During fertilization a new cell called the
zygote is formed. The zygote is the first body cell of the new
organism.
Types of Sexual Reproduction
Conjugation is when two cells come in contact with each other and
exchange small pieces (not all) of their genetic information. Example:
bacteria
Hermaphrodites are organisms that produced both male and female
sex cells. Example: tomato plants, sponges, and earthworms.
Separate sexes – males produce sperm cells and females produce
egg cells. Animals with separate sexes use one of two different ways
of fertilization.
External fertilization is when the sex cells unite outside the female’s
body. Example: fish, frogs…
Internal fertilization is when the male deposits sperm cells into the
female’s body to fertilize the egg cells. Example: Humans, dogs…
Reproduction in Flowering Plants
• Like animals, flowering plants have reproductive cells. These
reproductive cells are found in its flowers.
• The male sex cells, in flowers, are called pollen. Pollen is found in
the anthers which are located at the tips of the stamen.
• The female sex cells, in flowers, are called the eggs. The eggs are
found in the ovaries which are located at the base of the pistil.
• When
the pollen comes in contact with the egg cells it results in
fertilization, which is also known as pollination in plants.
• Most
plants need the pollen from a different plant (the same kind or
species of plant) in order for fertilization to occur. Fertilization from
plant to plant occurs in a couple different ways:
1. Pollen can travel by air.
2. Insects, bats and hummingbirds can help fertilize plants.
Seed and Fruit Formation
• The fertilized eggs (zygotes) of the flower become the seeds. The
petals eventually shrivel and fall off. The ovary in many plants
develops into the fruit. This fruit helps to protect and disperse the
seeds. Animals and birds eat the fruit. After the fruit has been
eaten the seeds are scatter around through the droppings of these
animals and birds.