Reproduction

T he Cell Theory The 4 main points of the cell theory are:  All living organisms are made of one or more cells  Cells are the basic unit of structure and function in all organisms  All cells come from previously existing cells  Organisms are controlled by single cells working together

Animal Cells

Plant Cells

So what’s the difference? Plant cells – rigid cell wall which provides structure and support for the cell Plant cells – have chloroplasts that enable them to make their own food through photosynthesis

Organelles A typical cell has many organelles, specialized structures that perform specific functions in the cell Nucleus – the control center of the cell Nuclear Membrane – encloses the cells genetic material or DNA (Deoxyribonucleic Acid) Nucleolus – darker area within the nucleus that makes ribosome parts

Cell Organelles Continued… Ribosomes – small, cell structures involved in the making of proteins Cell Membrane – the membrane that holds all the cell contents together Cytoplasm – the gel-like substance within the cell that supports the structures of the cell

Cell Organelles Continued… Endoplasmic Reticulum – transports materials to different parts of the cell Mitochondrion – an oval-shaped organelle that makes energy for a cell to use. The power-house of the cell Golgi Body – packages and moves (secretes) waste out of a cell Vacuole – stores water, food, wastes and other materials in the cell Lysosome – breaks down food, wastes and worn- out cell parts

Cell Division Part One: Mitosis

In the nucleus In non-dividing cells, the genetic material is stored as thin DNA super coils called CHROMATIN When a cell divides, the chromatin will shorten and thicken into CHROMOSOMES One strand of a double stranded chromosome is called a CHROMATID

Draw a double stranded chromosome. Label chromosome, chromatid and centromere Chromosome Chromatid Centromere Chromatid

Mitosis MITOSIS: a process by which the nucleus of a cell divides while maintaining the chromosome number  One cell  two cells  New cells have identical genetic material (DNA) of the parent cell Four stages of division (Prophase, Metaphase, Anaphase and Telophase - PMAT) plus a period of growth and metabolism called Interphase

The Cell Cycle

Phase One: Prophase Chromatin contracts and becomes visible (spaghetti). It is now called CHROMOSOMES Each is a double chromosome with a pair of SISTER chromatids which are joined to each other by a centromere Chromosomes begin to move towards the equator (center) of the cell Nuclear membrane disintegrates (breaks down) CENTRIOLES will form SPINDLE FIBERS that will attach to each centromere and move around the chromosomes

Prophase

Phase Two: Metaphase The centromeres of each chromosome line up along equator ( looks like praying hands) Centromeres divide so the doubled chromosomes become two identical single stranded sister chromatids Centrioles are now at the poles of the cell and are attached to each centromere by spindle fibers

Metaphase

Phase Three: Anaphase The spindle fibers begin to shorten and the chromosomes begin moving to opposite ends or poles of the cell (fingers) Each side gets one chromatid from each double stranded chromosome

Anaphase chromosomes

Phase Four: Telophase Begins when single stranded chromosomes reach the poles Chromosomes uncoil and turn into chromatin Nuclear membrane reappears Reverse of prophase Division of the cytoplasm or CYTOKINESIS is completed by pinching off in animals or by building a cell wall in plants

Telophase

Interphase Period between divisions Longest part of the cell cycle Cell is growing and metabolizing Nuclear membrane present Genetic information in the form of chromatin and cannot be seen with a microscope Before division each strand of DNA will replicate (copy) itself to become double stranded Near the end of interphase the DNA begins to condense (shorten)

Interphase

What’s the point of Mitosis? Mitosis creates identical copies of cells for:  1. growth  2. Repair/regeneration of damaged tissue  3. Asexual reproduction (animals) or vegetative reproduction (plants)

Asexual Reproduction Reproduction that involves only one parent; parent and offspring have identical genetics No special reproductive cells or organs used to create offspring Occurs through mitosis and cytokinesis Both single and multi-celled organisms, plants and simple animals can reproduce asexually In multi-cellular organisms, the offspring develop from undifferentiated, unspecialized cells from the parent Usually a rapid form of reproduction

Binary Fission Simplest form of asexual reproduction Parent divides into two approximately equal sized daughter cells Bacteria: circular chromosome attaches to plasma membrane then replicates, cell wall separates each copy Protozoa: eg. Amoeba become circular and use mitosis

Budding New individuals develop from small outgrowths of the parent (buds) May develop colonies (sponges) or break off to be individuals (hydra, yeast) Some organisms can both bud and reproduce sexually

Spores Specialized single cells that are released from the parent organism, germinate and grow by mitosis New cells differentiate to form a new organism Can reproduce quickly and in large quantities Often have thick protective coats Eg. Fungi, algae, protozoa

Regeneration The ability to regrow lost body parts Some animals can regrow entire new organisms from parts Ability to regenerate decreases as organisms increase complexity Even simple organisms that can regenerate entire organisms generally prefer to utilize a different method to reproduce

Vegetative reproduction MERISTEM: area on plant with unspecialized cells (cells that can become any kind of cell) that frequently divide using mitosis Meristematic cells can be found in the vegetative structures of a plant (roots, stems, leaves) Given proper treatment, meristem cells can reproduce mitoticlly then differentiate into new independent plants Structures include bulbs, corms, tubers, runners, rhizomes Can also be artificially propagated using cuttings, layerings or grafting

Bulb short underground stem with thickened storage leaves small new bulbs sprout from the old ones Eg. onions, tulips

Corm short underground stems with no fleshy leaves Eg. gladiolas, crocuses

Tuber enlarged part of an underground stem that contains stored food potatoes (eyes are tiny buds)

Runner AKA stolon is a stem that runs sideways and contains buds Eg. strawberry

Rhizome a stem that grows sideways under the ground ferns, irises

Cutting a stem, root or leaf cutting used to make a new plant

Layering part of a stem is bent and covered in soil once it roots the original can be cut off Eg. raspberries, roses

Grafting stem or bud removed from one plant and permanently joined to another plant Eg. grapes and many seedless fruits