REPRODUCTION Part 1

1. REPRODUCTIONPart 1 OCS Biology Mrs. Bonifay

2. Spontaneous Generation • Many years ago, some people thought living things could come from nonliving things. This is called spontaneous generation. For example, then they saw a frog jump out of a muddy pond, they thought the mud made the frog. • Spontaneous generation was proved to be untrue. Living things come from other living things.

3. DNA • Each organism’s cells contain the information needed to make another organism just like itself. Cells store this information as a chemical called DNA. • DNA stores information in a pattern of chemicals. • Your DNA contains all the information needed to make a human with your characteristics or traits.

4. DNA and Reproduction • Each type of organism has its own unique DNA. Humans have DNA about how to make a human. Frogs have DNA about how to make a frog. • When living things reproduce, they pass exact copies of their DNA to their offspring. • In some organisms, such as bacteria, reproduction requires one parent. The parent passes copies of all of its DNA to its offspring. Its DNA is identical to the parent’s DNA.

5. DNA & Reproduction • Reproduction in animals and plants usually involves two parents. • You have traits from both parents, even though you might resemble one parent more than the other. This is because your DNA is a combination of both parents’ DNA. Therefore, humans and other organisms produce offspring that are unique.

6. Diversity • Humans and other species that produce unique offspring are said to have diversity. • Diversity if the range of differences found in a certain population. • If a population’s environment changes suddenly, the population’s diversity can help it continue to survive. The population can adapt because of diversity. • Adaptations are traits that allow organisms to survive in certain environments. They are found in information on an organism’s DNA.

7. Asexual Reproduction • When an organism passes all of its DNA onto its offspring and the offspring are identical to the parent, it is called asexual reproduction. • One-celled organisms usually reproduce asexually. • Their cells divide to form two identical cells. • Protists, fungi, and some plants and animals can reproduce by asexual reproduction. • Skin cells, bone cells, and muscle cells are examples of human cells that reproduce asexually to form new cells. This allows your body to grow, heal, and replace dead cells.

8. Asexual Reproduction • One advantage of asexual reproduction is that an organism does not have to find a mate. • Another advantage is time. One-celled organisms can reproduce quickly. • A disadvantage of asexual reproduction is that the offspring are exact copies of their parent. The offspring lack diversity and are likely to respond to changes in environment. If change kills one offspring, it will likely kill them all.

9. Mitosis • In cells that have a nucleus, asexual reproduction occurs in the form of mitosis. • Mitosis is the dividing of the cell’s nucleus. • Before a cell undergoes mitosis, it makes a copy of its DNA. • DNA is found in the nucleus in rod-shaped structures called chromosomes. When DNA is copied, the chromosomes form pairs.

10. Sexual Reproduction • Humans and many other organisms have two parents. This is called sexual reproduction. • During sexual reproduction, a cell from one parent joins with a cell from the other parent. • A disadvantage of sexual reproduction is that an organism must find a mate.

11. Sexual Reproduction • Another disadvantage is sexual reproduction is that it usually takes longer to produce offspring. • A big advantage to sexual reproduction is that it leads to greater diversity in a population because each offspring is unique. • Sexual reproduction involves both a female, who produces egg cells, and a male, who produces sperm cells.

12. Sexual Reproduction • The gametes, or sex cell, of certain species contain one-half the number of chromosomes found in the species non-sex cells. • For example, human sex cells have 23 chromosomes in their nucleus. Human body cells have 46 chromosomes.

13. Meiosis • Gametes form by a division of the nucleus called meiosis. • Meiosis begins after the cell’s chromosomes have been copied. • During meiosis, the nucleus disappears. • The pairs of chromosomes line up in the center of the cell and then separate. A nucleus forms around each set of chromosomes.

14. Meiosis • Next, the cell divides into two new cells, and each new cell divides once again. Therefore, each original cell produces four sex cells. • Since cell division occurs twice, each sex cell contains one-half the number of chromosomes of the original cell.

15. Fertilization • Fertilization is the process by which a sperm cell and an egg cell join to form one cell. This cell is called a zygote, which has a complete set of chromosomes: half from the egg cell and half from the sperm cell. • When a female fish has laid her eggs under the water, a male fish swims above the eggs and releases billions of sperm into the water. One of the sperm will attach to one of the eggs, and its nucleus enters the egg joining with the nucleus of the egg cell. This is called external fertilization.

16. Fertilization • Most fish and amphibians use external fertilization. • All reptiles, birds, and mammals use internal fertilization. • Internal fertilization is when the male places sperm inside the female’s body where fertilization occurs.

17. Growth and Development • A new animal begins as a zygote (a single cell that contains a complete set of chromosomes). • Eventually, the zygote divides into millions of cells that make up an embryo. An embryo is an early stage in the development of an organism. In this process, the same DNA is copied in each cell.

18. Differentiation • An embryo’s cells gradually take on different shapes and functions. This is called cell differentiation.

19. Development • The embryos of many animals, such as fish, reptiles, and birds, develop inside an egg. • When young insects look like the adult, they are called nymphs. Nymphs cannot reproduce until they are adults.

20. Mammal Offspring • Mammals produce few offspring compared to fish and other kinds of animals. • Mammal parents often take care of their young for long periods of time, protecting them from danger and increasing their chances of survival. Because of this, fewer offspring are needed to ensure survival of a mammal species.

21. Mammal Offspring • Most animals do not lay eggs; the exceptions are the duck-billed platypus and the spiny anteater. • All other mammals carry their young inside their bodies, at least for part of the time. • Marsupials are mammals that give birth to young that are undeveloped. After being born, the tiny marsupial crawls into its mother’s external pouch, where it continues to develop. • All other mammals give birth to young ones that are more fully developed.

22. Food for Young Mammals • Most mammals embryos get food from inside their mother’s body. • Most female mammals have a uterus, an organ that holds and protects the developing embryo. • Inside the uterus, the embryo forms protectivetissues around itself. Part of these tissues form a placenta which provides food and oxygen from the mother’s body. • Once a young mammal is born, it feeds on milk produced by its mother’s mammary glands.

23. Food for Young Mammals • The embryos of most marsupials do not obtain food through a placenta. When inside the mother, it gets food from the fertilized egg for a short time, and then feeds on milk in the mother’s pouch after it is born. • For mammals that lay eggs, the mammal eggs do not contain a large food supply, so the young feed on milk from their mother’s mammaryglands after they are born.

24. Gestation • Different mammals have different gestation times, depending on the size of the animal. • Gestation time is the period of time from the fertilization of an egg until birth. • The larger the mammal, the longer the gestation times. • The gestation time for an elephant is almost two years; for a mouse, it is only 20 days.