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Cell Growth and Reproduction


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  • Uploaded On 25-07-2012

Cell Growth and Reproduction. Biology Agriculture. Cell Growth. All cells come in different sizes and shapes. Diffusion in fast and effective over short distances. It become slow and inefficient over long distances.

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Cell Growth and Reproduction

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Cell Growth and Reproduction

Biology Agriculture


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Cell Growth

  • All cells come in different sizes and shapes.

  • Diffusion in fast and effective over short distances.

    • It become slow and inefficient over long distances.

  • If a cell and a mitochondria 20cm in diameter – it would take months before it would receive molecules that entered the cell membrane.


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Cell Growth

  • Surface area-to-volume ratio

    • Area: the surface included in a set of lines.

    • Volume: space occupied as measured in cubic inches.

    • Ratio: the relationship in quantity, amount, or size between two or more things.


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Cell Growth

  • Due to the surface area-to-volume ratio cells divide before they become to large.

  • DNA is what directs the cell when it is becoming to large.


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Cell Reproduction

  • Cell division in necessary to form multi-cellular organisms.

  • Asexual Reproduction:

    • Production of offspring from one parent cell.

  • Sexual Reproduction:

    • Formation of offspring from the union of two gamete cells .


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Asexual Reproduction

  • Steps:

    • Chromosomes duplicate (called replication)

    • Both attach to a site located in the cell

    • They are forced apart.

      • Cell membrane constricts them till they separate.


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Asexual Reproduction

  • Some examples include:

    • Strawberry Runners

    • Potatoes

    • Star Fish


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Sexual Reproduction

  • Results from the joining of two highly specialized cells.

    • Sperm Cells

    • Ovum Cells or Egg Cell

  • Fertilization:

    • Sperm cell and ovum combine to form a Zygote.


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Chromosomes

  • Chromatids:

    • Long strands of DNA.

  • Chromosomes:

    • Made of two sister chromatids.

  • Held together by a centromere


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Diploid (2n) Cells

  • A cell with two of each kind of chromosomes are called Diploid Cells.


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Haploid (n) Cells

  • A cell with one kind of each chromosome is called a Haploid cell.


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Mitosis

  • Cells undergo mitosis as they reach their maximum cell size.

  • There are four steps in mitosis:

    • Prophase

    • Metaphase

    • Anaphase

    • Telophase


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Mitosis:

  • Stage 1 – Prophase.

  • Chromatids coil up into visible chromosomes.

  • Nucleus Disappears

  • Centrioles migrate to the polar ends of the cell

  • Spindle Fibers begin to form.


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Mitosis:

  • Stage 2 – Metaphase

  • Chromosomes become attached to the spindle fibers by their centromeres.

  • They are lined up across the center of the cell.


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Mitosis:

  • Stage 3 – Anaphase

  • Sister chromatids begin to separate

  • Chromatids are pulled apart, and separate from each other.


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Mitosis:

  • Stage 4 – Telophase

  • New cells prepare for their new existence.

  • Chromosomes uncoil and direct metabolic activity

  • Spindle Fibers break down

  • Nucleolus reappears

  • Double membrane forms between them


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Mitosis

  • Cytokinesis

    • Animals – Plasma Membrane pinches in along the equator of the cell.


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Mitosis

  • Cytokinesis

    • Plants - Cell Plate is laid across the equator.

    • Cell walls form around the plate


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Results of Mitosis

  • As a result,

    • Each daughter cell receives and exact copy of the chromosomes present in the parent cell.

    • They copy their chromosomes during Interphase.

    • They become a diploid cell 2n

    • The process can then start over.


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Results of Mitosis

  • Process that guarantees that genetic continuity.

  • The two new cells formed will carry out the same functions of the parent cell.

  • They will grow and divide just like the parent cells.


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Results of Mitosis

  • As a result of cell division we have groups of cells working together, until they create and organism, i.e.

    • Cells

    • Tissues

    • Organs

    • Organs Systems

    • Organisms


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The Cell Cycle

  • Cell Cycle:

    • The sequence of growth and division in the cell.

  • A cell goes though two periods:

    • A period of growth

    • A period of division


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The Cell Cycle

Prepare for cell division

2 hours

Mitosis 1 hour

DNA Synthesis and Replication

10 Hours

INTERPHASE

Rapid Growth and Metabolic Activity

9 hours


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Interphase

  • The busiest part of the cell cycle

    • Part I: Cell grows and protein production is high.

    • Part II: Cell copies its chromosomes

    • Part III: Parts manufactured for cell division.


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The Cell Cycle

  • The cell cycle is controlled by;

    • Proteins

    • Enzymes

    • Area – to – Volume Ratio

  • Occasionally, cells lose control.

    • Cancer, malignant growth resulting from uncontrolled cell division.


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Cancer – A mistake in the cell cycle!

  • Tumors

    • Masses of tissue that deprive normal cells of nutrients.

  • Cancer is the second leading cause of death in the United States, exceeded only by heart disease.


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Meiosis

  • Meiosis forms haploid daughter cells from diploid parent cells.

  • Meiosis is divided into two parts;

    • Meiosis I

    • Meiosis II


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Meiosis I

  • Synapsis

    • Homologous Chromosomes line up next to each other.

    • Forming a structure called a tetrad.


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Meiosis I

  • Meiosis I is divided into four stages;

    • Prophase I

    • Metaphase I

    • Anaphase I

    • Telophase I


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Meiosis I

  • Prophase I

    • Homologous Chromosomes are formed

    • Spindle fibers form

    • Tetrads are visible and have lined up along the equator.


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Meiosis I

  • Metaphase I

    • Each tetrad becomes attached to the spindle fibers


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Meiosis I

  • Anaphase I

    • Homologous chromosomes are pulled apart.

    • One pair goes to the on polar end while the other goes to the other end.


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Meiosis I

  • Telophase I

    • Cytokinesis takes place.

    • The cell divides.


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Meiosis I

  • At the end of Meiosis I;

    • One chromosome from each parent cell is present in the daughter cell.

  • Meiosis I is a reductive division;

    • Reduce the chromosomes from diploid (2n) to a haploid (n).


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Meiosis II

  • Each daughter cell produced in Meiosis I undergoes another division.

  • Meiosis II is very similar to Mitosis except, it is not proceeded by a replication of the chromosomes.


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Meiosis II

  • There are four stages;

    • Prophase II

    • Metaphase II

    • Anaphase II

    • Telophase II


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Meiosis II

  • Resulting in;

    • Four daughter cells

    • Each daughter cell produced is haploid.

    • Each cell has four chromosomes.

    • One from each of the homologous pairs of parent cells.


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Meiosis II

  • Prophase II

    • New spindle fibers formaround the chromosomes.


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Meiosis II

  • Metaphase II

    • Chromosomes line up along the equator.

    • Attach the centromere to the spindle fibers


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Meiosis II

  • Anaphase II

    • The centromere divides and the chromatids separate.

    • Each chromatids becomes it on chromosomes with their own centromere.


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Meiosis II

  • Telophase II

    • The nuclear envelope forms around each set of chromosomes.

    • Cell undergoes Cytokinesis.


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Meiosis – Why?

  • The result;

    • Cells used for reproduction

      • Sperm Cells

      • Ovum Cells