Download Lesson`s Notes Unit 3 lesson 1

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.
• Scientists developed the cell theory that states: all
living things are made of cells, all life processes take
place in cells, and new cells come from existing cells.
• Robert Hooke was the first person to study cells
using a microscope.
Copyright © Houghton Mifflin Harcourt Publishing Company
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
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
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
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.
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 3 Lesson 1 What Are Cells?
How Cells Divide
• Then, the copied chromosomes separate and
move to opposite ends of the cell.
• A nuclear membrane is formed around each
set of chromosomes.
• 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
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
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
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
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