Cells The Building Blocks of Life: Cell Division and Reproduction

All living things are made of cells Plant CellsAnimal Cells

Cell Theory The current cell theory states that: –A–All living things are made of cells. –C–Cells are the basic unit of structure and function in living things. –L–Living cells only come from other living cells.

What Are Cells Made Of? Organelles, or “tiny organs”, are the structures that make up a cell. Organelles were discovered by Robert Hooke in 1665 while looking at cork cells. –N–N–N–Nucleus, mitochondria, chloroplasts, cell wall, cell membrane, lysosomes, vacuoles, ribosomes, cytoplasm, etc.

What are Chromosomes? Chromosomes are found in the nucleus of the cell. –C–Chromosomes are made of DNA = genetic material that directs the cell’s activities. DNA codes for traits and is passed on from parent to offspring (in both sexual and asexual reproduction) –A–All organisms have a characteristic number of chromosomes. Humans have 46 chromosomes (2N) Chromosomes are arranged in pairs: 23 pairs (N = ½ the number of chromosomes; 1 from each pair)

How Do Cells Grow? Cells do not grow in size. Why Not? Instead cells grow by increasing their numbers. cell division –This process is called cell division.

Cell Division Cell division occurs in a series of stages or p pp phases. The most important concept is that: –A–A–A–A parent cell divides into two daughter cells.

Two Types of Cell Division Mitosis forms identical daughter cells Meiosis forms daughter cells with half the chromosomes of parent cell

Cell Division Cells can divide in two ways: Mitosis 1 division 2 daughter cells Genetically identical to parent cells Can result in new individuals Meiosis 2 divisions 4 daughter cells = gametes (sperm and egg) ½ the number of chromosomes as parent cells 1 st step in reproduction – next is fusion of gametes

Cellular Reproduction

Why is Reproduction Needed? Cell reproduction is necessary to: –keep the species going –replace the death of cells –increase the size of organisms (due to size limit of cells) –produce new individuals.

2 Forms of Reproduction Asexual Reproduction Mitosis A single parent No special sex cells No special sex organs Genetically identical to parents Sexual Reproduction Meiosis 2 parents Special sex cells = gametes (sperm/egg) Special sex organs = gonads (ovaries/testes) Not genetically identical to parent (1/2 chromosomes from mom, ½ from dad)

Mitosis – Asexual Reproduction Result is two identical cells

Meiosis - Sexual Reproduction Result is daughter cells with half the chromosomes

Egg and Sperm Cells – Fertilization Fertilization is the fusion of two cells, a sperm cell and an egg cell.

What are the Phases of Cell Division Phase 1: Interphase Phase 2: Prophase Phase 3: Metaphase Phase 4: Anaphase Phase 5: Telophase Phase 6: Cytokinesis

Cell Division – Interphase: Chromosomes are Copied Chromosomes look threadlike – called chromatin.Chromosomes look threadlike – called chromatin. Centrioles appear outside the nucleus.Centrioles appear outside the nucleus. Near the end of phase 1 cell division begins:Near the end of phase 1 cell division begins: –Chromosomes are copied

Interphase

Cell Division – Prophase: Mitosis Begins Mitosis is the process of cell division where the nucleus divides into two nuclei and two identical daughter cells are formed.

Prophase

Cell Division – Metaphase: Chromosomes attach to spindle In metaphase the chromosomes attach themselves to the spindle fibers.In metaphase the chromosomes attach themselves to the spindle fibers. The centromere is what attaches the chromosomes to the spindle fiber.The centromere is what attaches the chromosomes to the spindle fiber.

Metaphase

Cell Division – Anaphase: Chromosomes begin to separate In anaphase the chromosomes begin to separate.In anaphase the chromosomes begin to separate. The centromere splits and each pair of chromatids begin to move toward the ends of the cell.The centromere splits and each pair of chromatids begin to move toward the ends of the cell.

Anaphase

Cell Division – Telophase Two new nuclei form In telophase two new nuclei form Chromosomes uncoil and are surrounded by a nuclear membrane. A nucleolus reappears. Cell division is complete.

Animal and Plant Telophase

Cell Division – Cytokinesis Two daughter cells form In Cytokinesis two new daughter cells form.In Cytokinesis two new daughter cells form. Cell membrane “pinches” cell in the middle forming two identical daughter cells.Cell membrane “pinches” cell in the middle forming two identical daughter cells. –In plant cells a cell wall forms around each daughter cell. Process of cell division is now over.Process of cell division is now over.

Plant Cell Cytokinesis

Cell Reproduction: Key Terms Cell = the basic building block of all living things Organelles = tiny organs, structures, that make up a cell and are responsible for cell function. Chromosomes = genetic material found in the nucleus that directs the cell’s activities, made of DNA. Cell division = the process of cell reproduction where a parent cell creates new daughter cells.

Cell Reproduction: Key Terms Mitosis = cell division that results in two daughter cells that are genetically identical to parent. Meiosis = cell division that results in 4 daughter cells, each having ½ the chromosomes of the parent. Asexual reproduction = process where a new individual organism is created from only one parent; offspring is genetically identical to parent.

Cell Reproduction: Key Terms Sexual reproduction = process where a new individual organism is created from two parents; offspring is not genetically identical to parent. Gametes = specialized sex cells involved in sexual reproduction (male = sperm, female = egg) Gonads = specialized sex organs where gametes are created by meiosis (male = testis, female = ovaries) Fertilization = the fusion of gametes that results in the formation of a new organism, or offspring.

Cell Reproduction: Key Terms Internal fertilization = fertilization that takes place inside an organism. External fertilization = fertilization that takes place outside an organism.

What Is Cell Specialization? In multicellular organisms, cells not only complete its own life activities, but also performs a function that contributes to the life of the organism. Within multicellular organisms there is division of labor or specialization. –T–T–T–The work of keeping the organism alive is divided up among different parts of the organism.

Levels of Specialization Cells combine to form Tissues combine to form Organs combine to form Organ systems combine to form Organism

More Specialization Students combine to form Classes combine to form Grades combine to form Schools combine to form District

What are Tissues? TissuesTissues are cells that are similar in structure and function that combine together. –Example: bone cells form bone tissue –Other examples: muscle tissue, nerve tissue, connective tissue.

Bone Tissue and Muscle Tissue

What are Organs? Organsare groups of different tissues that work together.Organs are groups of different tissues that work together. –Example: the heart is an organ made of muscle tissues and blood tissue –Other organs: brain, stomach, skin

Organs – Heart and Stomach

What are Organ Systems? Organ systems are a group of organs working together to perform a specific function for the organism. –E–Examples: skeletal system, muscular system, digestive system.

Organ Systems

What are Organisms? OrganismsOrganisms are an entire living thing that carries out all the basic life functions. –Examples: Humans, cat, fish, fly

Some Organisms