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Cell Theory & Asexual Reproduction

Gr 9 Science
by

Ms. Wall

on 6 May 2013

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Transcript of Cell Theory & Asexual Reproduction

The Cell Theory Organelles The Cell Cycle Mitosis Asexual Reproduction in Humans Animal Cells Vs Plant Cells •Plant cells also contain chloroplasts, which in turn contain chlorophyll, which chemically changes sunlight into food energy, aka “Photosynthesis” •the cell is the basic unit of life
•we know this because all life functions can be completed by each individual cell (using energy, eliminating wastes, responding to changes in the environment, building body parts, storing genetic information, and reproducing)
•100 trillion cells in the body
•All life started from one cell
•The formal cell theory is what we used to explain all of the observations of living things today The Cell Theory & Asexual Reproduction
•Instead of each cell growing bigger and bigger, they divide to make new cells that are the same size

•Every second, millions of cells in your body are reproduced

•Most cells show remarkable similarities in how they grow and divide
Original nucleus separates the information that it has and becomes 2 identical nuclei

When it is finished there is 1 cell with 2 nuclei, (This is called replication). The cell is now ready to begin Mitosis.

There are 4 phases to mitosis: prophase, metaphase, anaphase, telophase

Cytokinesis begins when mitosis is almost finished (during telophase). **Humans have 46 chromosomes in each cell of their body (except sex cells which have 23)**
We have seen that most organisms that are single-celled, rely solely on asexual reproduction. Humans use asexual reproduction, but not to make their offspring.
Asexual reproduction happens in every cell in the human body, except in the ovaries and testes where sex cells are made (example: making new skin cells happens by asexual reproduction). Asexual Reproduction in Humans and Animals There are 4 parts to the cell theory:
1. All living organisms are made up of one or more cells
2. Cells are the basic units of structure and function in all organisms
3. All cells come from previous existing cells
4. The total activity of an entire organism depends on the activity of each independent cell The Cell Theory
-Are specialized structures inside of a cell
-Each has its own special job
-Each organelle is surrounded by a membrane
-These membranes are important because they allow several different processes to happen at the same time •Animal cells have no structure to act as a skeleton. A skeleton of bone supports the organism. In plants there are no bones or skeletal structure; therefore the cells must provide the support. A plant cell contains a sturdy cell wall, which animal cells do not have. Nucleus: has the role of coordinating the activity of the organelles, but has the primary function that it contains all the genetic info (DNA) required for reproduction. Deoxyribonucleic Acid = DNA is the life of a cell
Average human cell has 2 cycles of 20 hours
2 parts of a cycle: growth and division •Cell Cycle Growth Also known as interphase
Majority of time in cells is spent on growing
Here the cells grow and prepare for division
Genetic information is copied so there are 2 sets of DNA Division Where new cells are made from 1 original cell
After cell division is complete, there are 2 new cells that are identical to the original cell
There are 2 parts to cell division: mitosis and cytokinesis Divides nuclear material, or its chromatin. (Chromatin is loose DNA). It forms double stranded chromosomes, joined at a single point called the centromere. Double stranded chromosomes are now large, dense, and easily visible with a microscope. The nuclear membrane disintegrates, and spindle fibres form from the centrioles. Prophase: The tugging action of the spindle fibres, pulling on the chromosomes into a line in the centre of the cell. Metaphase Separation begins.
Spindle fibers contract and shorten.
They pull the centromeres apart.
Half of the chromosomes are pulled to opposite sides of the cell.
Each half has identical single stranded chromosomes. Anaphase Telophase One complete set of chromosomes are at opposite sides of the cell.
Spindle fibres disappear.
Nuclear membrane forms around the chromosomes
The cell gets ready to divide, and cytokinesis is about to begin.
Cytokinesis – pinching of the cell
You have two separate cells each with half of the original DNA. Cytokinesis Also known as cytoplasmic division
Separation of cytoplasm and organelles
Starts before mitosis is complete, with the “pinching in” of the cell, during telophase.
1 cell physically splits into 2 cells
Cytokinesis is different in plant and animal cells, because plant cells have cell walls.
Cell plate (plants) – is the plate in the centre of the cell Overview of Mitosis Where does cytokinesis take place? The phase that happens before and after mitosis
Cell spends most of its life in this phase
Occurs between mitotic divisions
Also known as the resting state
Cells undergo normal processes and functions
The cells grow, and replicate it’s DNA, then prepares for phase 1 of mitosis Interphase Anagram: IPMAT Asexual Reproduction Asexual reproduction is the formation of a new individual that has identical genetic information to its parent. It is the formation of a new individual from a single organism. It happens by mitosis. It is an effective method to quickly produce new cells that are exactly the same as the parent cells. Humans, bacteria, fungi, some animals, and plants reproduce asexually in the following ways: Regeneration Skin and bone cells can undergo mitosis, and can heal themselves eventually. Repairing of injured cells or the making of lost body parts is called Regeneration.
For example: lizard’s tails, sea stars, worms, etc.
The accidentally severed fingertip of a child may regrow if this happens before puberty. Complete Sea Stars Scenario Normal Cell Replacement
Stomach cells- 2 days
Intestinal - 3 days
Oral Tissues - 3-10 days
Skin cells - 20 days
Blood cells - 120 days
Liver cells - 200 days
Brain cells - 30-50 years Aging and dying •Occurs when cells are being replaced slower, or not at all. Example: wrinkling. •Dying takes place when net cell loss is greater than replacement. •Things that instruct the cells to “go wild” by changing the DNA are: ultraviolet radiation, carcinogenic chemicals, asbestos, Tobacco, radioactivity, and some viruses. Cell cycle out of control •When cells reproduce at an accelerated rate, this is considered cancerous tissue. •Local and non-spreading growth is known as a benign tumour or lesion. This is the “good cancer”. •Malignant or metastatic tumour is a cancerous growth that has and/or will spread to the other areas of the body, through the blood or lymphatic systems. Causes of cancer In the kingdom Animalia, animals are divided into two main groups. Vertebrates- animals with backbones, and invertebrates- animals without backbones.
Many invertebrates, like jellyfish, worms, shellfish, insects, etc. reproduce asexually to form one or more identical offspring from a single parent. Regeneration: As seen before, some types of animals like starfish, sea cucumbers, and planaria (or flat worm), can regenerate themselves. Planaria reproduce by splitting themselves, and regenerating the piece that’s missing. Budding: Animals such as sponges and hydras reproduce asexually by budding. A cell, usually near base of the organism, undergoes mitotic division, (or mitosis), repeatedly, in order to create a new bud. When the bud completes its development, it will detach and become its own organism. For more details, see budding in Fungi. Asexual Reproduction in Bacteria Members of the “Monera” kingdom, (ex: bacteria, amoeba) are one-celled organisms that do not contain a true nucleus.
Bacteria reproduces asexually, through a process called binary fission.
Binary fission is where the parent cell (or original cell), divides so that each new cell contains a single chromosome carrying a complete set of DNA.
The new cell created is identical to the parent cell.
Binary fission is the simplest form of asexual reproduction, and can be completed within 20 minutes. Complete Infection activity Asexual Reproduction in Fungi Mould, yeast, and mushrooms are all members of the fungi kingdom.
The three methods that fungi use to reproduce asexually are: Fragmentation, budding, and spores. Fragmentation A small piece, or fragment, breaks away from the main mass, and grows into a new individual. (Very similar to regeneration) Budding Yeast is often used to make bread. Yeast reproduce asexually by a process called budding.
First, a copy of the nucleus is created.
Then, a small outgrowth, (or bud), forms on the cell wall.
This bud, containing the new nucleus, grows on the cell wall, until it eventually breaks off to become a single, independent cell. Spore formation A parent cell undergoes many cell divisions and contains casings that contain thousands of spores.
Spores are thread-like projections that root themselves into whatever they land on.
When the spore case is large enough it will break releasing thousands of spores.
Imagine a dandelion weed, blowing in the wind.
If the temperature, moisture, and landing location is right, a new plant is produced.
The most common example is bread mould. Asexual Reproduction in Plants The tips and roots of plants are growing areas, filled with cells called meristematic cells.
These meristem areas are unspecialized cells with only one purpose: to undergo mitosis and cell division repeatedly.
If part of the plant structure becomes damaged, meristem cells are activated and start repairing the structure.
Plant growers use multiple different techniques to grow and reproduce plants/crops. They are through cloning, roots, runners, layering and grafting. Cloning: When you snip plants from a “parent stem” and soak them in water for a few weeks, roots may grow from the bottom of the stem, allowing you to then transfer it to soil, having created a new identical plant. This process is called cloning. Roots: Plants like dandelions and asparagus, grow from their roots. If the root is left in the ground, the plant will continue to grow. Plant sellers can then simply sell the roots, instead of the whole plant. Runners: Some plants have special stems called “runners” that reproduce a new plant with identical genetic information. Strawberry plants are good examples of this. Layering: Plants like blackberry, raspberry, and rose bushes can be “layered” under soil, and will sprout new roots. Once a strong root system is established, the plant can be transferred to a new location. Grafting: This is a technique used by growers to create types of plants with different characteristics. When a plant has strong roots, a scion (a different plant with similar characteristics), can be attached by grafting, to create a new plant. This is how McIntosh apples are grown. This is commonly used with apples, grapes, and roses.
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