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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.