chapter: cells—the units of life table of contents section 1: the world of cells section 2: the...

Chapter: Cells—The Units of Life

Table of ContentsTable of Contents

Section 1: The World of Cells

Section 2: The Different Jobs of Cells

• A cell is the smallest unit of life in all living things.

• Different cells have different jobs in living things.

Importance of Cells

The World of CellsThe World of Cells

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• Cells are important because they are organized structures that help living things carry on the activities of life.

• The three main ideas of the cell theory are:

Cell Theory


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1. All living things are made of one or more cells.2. The cell is the basic unit of life in which the activities of life occur.3. All cells come from cells that already exist.

• The smallest organisms on Earth are bacteria.

The Microscopic Cell


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• They are made up of only one cell.

• Larger organisms are made many cells.

The Microscopic Cell


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• These cells work together to complete all of the organism's life activities.

• Your body contains more than 10 trillion (10,000,000,000,000) cells.

• Better microscopes have helped scientists learn about the differences among cells.

Microscopes


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• The microscope used in most classrooms is called a compound light microscope.

• In this type of microscope, light passes through the object you are looking at and then through two or more lenses.

Microscopes


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• The lenses enlarge the image of the object.

• How much an image is enlarged depends on the powers of the eyepiece and the objective lens.

Microscopes


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• A power of 10 X means that the lens can magnify something to ten times its actual size.

• The magnification of a microscope is found by multiplying the powers of the eyepiece and the objective lens.

What are cells made of?


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• As small as cells are, they are made of even smaller parts, each doing a different job.

What are cells made of?


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Outside the Cell


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• The cell membrane is a flexible structure that holds the cell together.

• The cell membrane forms a boundary between the cell and its environment.

Outside the Cell


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• Some cells also have a structure outside the cell membrane called a cell wall.

• The cell wall helps support and protect these cells.

Inside the Cell


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• The inside of a cell is filled with a gelatinlike substance called cytoplasm (SI tuh pla zum).

• Approximately two-thirds of the cytoplasm is water, but it also contains many chemicals that are needed by the cell.

Organelles


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• Except for bacterial cells, cells contain organelles (or guh NELZ).

• These specialized cell parts can move around in the cytoplasm and perform activities that are necessary for life.

Organelles


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The Nucleus


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• In the cells of organisms except bacteria, the hereditary material is in an organelle called the nucleus (NEW klee us).

The Nucleus


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• Inside the nucleus are chromosomes (KROH muh zohmz).

• Chromosomes contain an important chemical called DNA. It determines which traits an organism will have.

Storage


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• In cells, food, water, and other substances are stored in balloonlike organelles in the cytoplasm called vacuoles (VA kyuh wohlz).

• Some vacuoles store wastes until the cell is ready to get rid of them.

Energy and the Cell


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• Cells, except bacteria, have organelles called mitochondria (mi tuh KAHN dree uh).

• An important process called cellular respiration takes place inside a mitochondrion.

Energy and the Cell


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• Cellular respiration is a series of chemical reactions in which energy stored in food is converted to a form of energy that the cell can use.

Energy and the Cell


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• This energy is released as food and oxygen combine.

• Waste products of this process are carbon dioxide and water.

Nature's Solar Energy Factories


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• Animals obtain food from their surroundings.

• Plants, algae, and many types of bacteria make food through a process called photosynthesis (foh toh SIHN thuh sus).



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• Most photosynthesis in plants occurs in leaf cells.

• Inside these cells are green organelles called chloroplasts (KLOR uh plats).



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• During plant photosynthesis chloroplasts capture light energy and combine carbon dioxide from the air with water to make food.

• As the plant needs energy, its mitochondria release the food's energy.

11Section CheckSection Check

Question 1

Which part of the cell protects the cell and gives it shape?

Answer

Cell walls are tough, rigid outer coverings that protect the cell and give it shape. The cells of plants, algae, fungi, and most bacteria are enclosed in a cell wall.


Question 2

Which is a one-celled organism?

A. bacteriaB. fungiC. plantD. turtle

11Section CheckSection CheckSection CheckSection Check

Answer

The answer is A. Bacteria are made up of only one cell.


Question 3

Where is food energy changed into a form of energy that a cell can use?

A. chloroplastB. nucleusC. mitochondrionD. vacuole

11Section CheckSection CheckSection CheckSection Check

Answer

The correct answer is C. Mitochondria are bean-shaped organelles.

Special Cells for Special Jobs

• Cells that make up many-celled organisms, like you, are specialized.

• Different kinds of specialized cells work as a team to perform the activities of a many-celled organism.

The Different Jobs of CellsThe Different Jobs of Cells

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Types of Human Cells

• Your body is made up of many types of specialized cells.

• A cell's shape and size can be related to its function.


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Types of Plant Cells

• Plants also are made of several different cell types.

• Plants have different types of cells in their leaves, roots, and stems.


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Types of Plant Cells

• Some cells in plant stems are long and tubelike. Together they form a system through which water, food, and other materials move in the plant.

• Other cells are smaller or thicker. They provide strength to the stems.


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Cell Organization

• Many-celled organisms are not just mixed-up collections of different types of cells.

• Cells are organized into systems that, together, perform functions that keep the organism healthy and alive.


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Tissues and Organs

• Cells that are alike are organized into tissue (TIH shewz).

• Tissues are groups of similar cells that all do the same sort of work.


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Blood is a Tissue

Tissues and Organs

• Different types of tissues working together can form a structure called an organ (OR gun).

• The stomach is an organ that includes muscle tissue, nerve tissue, and blood tissue.


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• Other human organs include the heart and the kidneys.

Organs Systems• A group of organs that work together to do

a certain job is called an organ system. • Organ systems found

in your body include the respiratory system, the circulatory system, the reproductive system, and the nervous system.


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Click box to view movie.

Organs Systems

• Organ systems also work together.

• For example, the muscular system has more than 600 muscles that are attached to bones.


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• The contracting cells of muscle tissue cause your bones, which are part of the skeletal system, to move.


Question 1

A cell’s shape is often related to its _______.

A. functionB. originC. organizationD. size


Answer

The correct answer is A. A cell’s shape and size can be related to its function.


Question 2

Which is the correct order of cell organization?

A. cell, tissue, organ system, organB. cell, organ, tissue, organ systemC. cell, tissue, organ, organ systemD. tissue, cell, organ, organ system


Answer

The answer is C. Cells are organized into systems that, together, perform functions that keep the organism alive.


Question 3

Which is long and has many branches, allowing it to receive and deliver messages quickly?

A. bone cellB. fat cellC. muscle cellD. nerve cell


Answer

The correct answer is D. Nerve cells are long and have many branches.

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End of Chapter Summary File

chapter: cells—the units of life table of contents section 1: the world of cells section 2: the...

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