Unit 3 Lesson 1 What Are Cells? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 1 What Are Cells? All Made of Cells Cells are the basic units of structure and function in a living thing. The bodies of all living things are made up of cells, including nerve and skin cells. Living things are also called organisms and can be made up of one cell or trillions of cells. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 1 What Are Cells? All Made of Cells People did not know cells existed because cells were microscopic, or not visible without a microscope. Cell theory 1. all living things are made of cells 2. all life processes take place in cells 3. new cells come from existing cells. Robert Hooke - first person to study cells using a microscope Copyright © Houghton Mifflin Harcourt Publishing Company

What Parts Do Cells Have? Unit 3 Lesson 1 What Are Cells? What Parts Do Cells Have? Plants and animals are made of cells, but they need different cell parts to stay alive. The nucleus makes more cells, produces energy, takes in materials, and gets rid of wastes. Cell membranes control what enters and leaves the cell. Mitochondria release energy that the cells use to do their jobs. The jellylike cytoplasm gives the cell shape and holds the cell parts together. Copyright © Houghton Mifflin Harcourt Publishing Company

What Parts Do Cells Have? Unit 3 Lesson 1 What Are Cells? What Parts Do Cells Have? The cell wall protects plant cells and helps the plant keep its shape. The chloroplast uses the sun’s energy to make sugar to feed the plant. The vacuole in a plant cell stores water, nutrients, and waste. In animal cells, the vacuole is much smaller. Copyright © Houghton Mifflin Harcourt Publishing Company

Cells Divide and Multiply Unit 3 Lesson 1 What Are Cells? Cells Divide and Multiply Cell division makes two cells from one. Cells divide for two reasons: to grow and reproduce. As cell division occurs, the organism grows. When organisms reproduce, they make egg and sperm cells through cell division. Copyright © Houghton Mifflin Harcourt Publishing Company

Cells Divide and Multiply Unit 3 Lesson 1 What Are Cells? Cells Divide and Multiply Chromosomes are structures in the cell’s nucleus made of DNA. DNA is made of sections called genes. Genes control an organism’s characteristics. An organism’s characteristics, such as height or eye color, come from the parent’s cells when they reproduce. Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 1 What Are Cells? How Cells Divide *Mitosis is a six-step process that allows the organism to grow. *Each chromosome is copied before the cell divides. Copies of each chromosome are joined. The duplicated chromosomes move to the middle of the cell. 4. Then, the copied chromosomes separate and move to opposite ends of the cell. 5. A nuclear membrane is formed around each set of chromosomes. 6. Finally, the cytoplasm divides and cell division is complete! Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 3 Lesson 1 What Are Cells? How Cells Divide *Meiosis forms eggs and sperm, or sex cells, which have half as many chromosomes as body cells. Egg and sperm cells join to form a new single cell during sexual reproduction. The single cell divides by mitosis and grows into a new individual. Copyright © Houghton Mifflin Harcourt Publishing Company

Where Do Traits Come From? Unit 3 Lesson 1 What Are Cells? Where Do Traits Come From? *Inherited traits are characteristics passed from parents to their offspring. *Examples of these characteristics might include eye color, hair color, freckles, and face shape in humans, and fur color and texture in animals. Copyright © Houghton Mifflin Harcourt Publishing Company

Where Do Traits Come From? Unit 3 Lesson 1 What Are Cells? Where Do Traits Come From? Meiosis causes genetic differences since an organism receives only half of its genes from each parent. This results in genetic differences between parents and offspring. Copyright © Houghton Mifflin Harcourt Publishing Company

Dominant and Recessive Traits Unit 3 Lesson 1 What Are Cells? Dominant and Recessive Traits In the 1800s, Gregor Mendel observed height differences in pea plants. Mendel investigated how the height trait was passed on from parent plants. Copyright © Houghton Mifflin Harcourt Publishing Company

Dominant and Recessive Traits Unit 3 Lesson 1 What Are Cells? Dominant and Recessive Traits *Mendel hypothesized that traits in organisms are controlled by a pair of factors and each parent passes on one factor. *In the pea plants, tallness was a strong, or dominant trait. Shortness was a weak, or recessive trait. Copyright © Houghton Mifflin Harcourt Publishing Company