Chapter 8:

Cellular

Transport and

the Cell Cycle

Chapter Intro-page 194

What You’ll Learn

You will discover how molecules are transported across the plasma membrane.

You will sequence the stages of cell division.

You will identify the relationship between the cell cycle and cancer.

8.1 Section Objectives – page 195

• Explain how the processes of diffusion, passive transport, and active transport occur and why they are important to cells.

Section Objectives:

• Predict the effect of a hypotonic, hypertonic, or isotonic solution on a cell.

Section 8.1 Summary – pages 195 - 200

• Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

Osmosis: Diffusion of Water

• In a cell, water always moves to reach an equal concentration on both sides of the membrane.

Section 8.1 Summary – pages 195 - 200

• The diffusion of water across a selectively permeable membrane is called osmosis.

Osmosis: Diffusion of Water

• Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.

Section 8.1 Summary – pages 195 - 200

• Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis.

What controls osmosis?

Before Osmosis

After

Osmosis

Water molecule

Sugar molecule Selectively permeable membrane

Section 8.1 Summary – pages 195 - 200

• Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions.

Cells in an isotonic solution

H2O

H2O

Water Molecule

Dissolved Molecule

Section 8.1 Summary – pages 195 - 200

Cells in an isotonic solution

• In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.

H2O

H2O

Water Molecule

Dissolved Molecule

Section 8.1 Summary – pages 195 - 200

Cells in an isotonic solution

• In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.

H2O

H2O

Water Molecule

Dissolved Molecule

Section 8.1 Summary – pages 195 - 200

Cells in an isotonic solution

• A plant cell has its normal shape and pressure in an isotonic solution.

Section 8.1 Summary – pages 195 - 200

Cells in a hypotonic solution

• In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.

H2O

H2O

Water Molecule

Dissolved Molecule

Section 8.1 Summary – pages 195 - 200

Cells in a hypotonic solution

• Plant cells swell beyond their normal size as pressure increases.

Section 8.1 Summary – pages 195 - 200

Cells in a hypertonic solution

• In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink.

H2O

H2O

Water Molecule

Dissolved Molecule

Section 8.1 Summary – pages 195 - 200

Cells in a hypertonic solution

• Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

Section 8.1 Summary – pages 195 - 200

Active Transport

• Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell.

Plasma membrane

Concentration gradient

Carrier proteins

Cellular energy

Step 1 Step 2

Section 8.1 Summary – pages 195 - 200

Transport of Large Particles

• Endocytosis is a process by which a cell surrounds and takes in material from its environment.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes

Section 8.1 Summary – pages 195 - 200

Transport of Large Particles

• The material is engulfed and enclosed by a portion of the cell’s plasma membrane.

Exocytosis

Digestion

Nucleus

Wastes

Endocytosis

Section 8.1 Summary – pages 195 - 200

Transport of Large Particles

• The resulting vacuole with its contents moves to the inside of the cell.

Exocytosis

Digestion

Nucleus

Wastes

Endocytosis

Section 8.1 Summary – pages 195 - 200

Transport of Large Particles

• Exocytosis is the expulsion or secretion of materials from a cell.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes

Section 8.1 Summary – pages 195 - 200

Transport of Large Particles

• Endocytosis and exocytosis both move masses of material and both require energy.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes

Section 2 Objectives – page 201

Section Objectives

• Relate the function of a cell to its organization in tissues, organs, and organ systems.

• Sequence the events of the cell cycle.

22 Cell Growth

& Reproduction

Egg & sperm

Section 8.2 Summary – pages 201 - 210

Cell Size Limitations

• The cells that make up a multicellular organism come in a wide variety of sizes and shapes.

• Considering this wide range of cells sizes, why then can’t most organisms be just one giant cell?

Section 8.2 Summary – pages 201 - 210

Diffusion limits cell size

• Although diffusion is a fast and efficient process over short distances, it becomes slow and inefficient as the distances become larger.

• Because of the slow rate of diffusion, organisms can’t be just one giant-sized cell.

Section 8.2 Summary – pages 201 - 210

DNA limits cell size

• The cell cannot survive unless there is enough DNA to support the protein needs of the cell.

• In many large cells, more than one nucleus is present.

• Large amounts of DNA in many nuclei ensure that cell activities are carried out quickly and efficiently.

Section 8.2 Summary – pages 201 - 210

Surface area-to-volume ratio

• As a cell’s size increases, its volume increases much faster than its surface area.

Surface area = 6 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 mm

4 mm

Section 8.2 Summary – pages 201 - 210

Surface area = 6 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 mm

4 mm

• If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete.

Surface area-to-volume ratio

Section 8.2 Summary – pages 201 - 210

• The surface area, however, would increase by a factor of only four.

Surface area-to-volume ratio

Surface area = 6 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 mm

4 mm

Section 8.2 Summary – pages 201 - 210

Surface area-to-volume ratio

Surface area = 6 mm2 Volume = 1 mm3

Surface area = 24 mm2 Volume = 8 mm3

1 mm 1 mm

1 mm

2 mm 2 mm

2 mm

4 mm 4 mm

4 mm

• The cell would either starve to death or be poisoned from the buildup of waste products.

Section 8.2 Summary – pages 201 - 210

Cell Reproduction

• Cell division is the process by which new cells are produced from one cell.

• Cell division results in two cells that are identical to the original, parent cell.

ASEXUAL

REPRODUCTION

• New organisms from 1 parent

• Fission-splitting-into 2 parts

• spore production-plants

• budding-cells pinch free

• cloning- cell placed in nutrient & exact duplicate is formed

• Regeneration- replacement of lost parts- repair damaged

Section 8.2 Summary – pages 201 - 210

The discovery of chromosomes

• Structures, which contain DNA and become darkly colored when stained, are called chromosomes.

• Chromosomes are the carriers of the genetic material that is copied and passed from generation to generation of cells.

• Accurate transmission of chromosomes during cell division is critical.

Section 8.2 Summary – pages 201 - 210

The structure of eukaryotic chromosomes

Centromere

Chromosome

Sister chromatids

Supercoil within chromosome

Continued coiling within supercoil

Histone H1

Nucleosome

DNA

Section 8.2 Summary – pages 201 - 210

The Cell Cycle

• The cell cycle is the sequence of growth and division of a cell.

• The majority of a cell’s life is spent in the growth period known as interphase.

Interphase

Section 8.2 Summary – pages 201 - 210

The Cell Cycle

• Following interphase, a cell enters its period of nuclear division called mitosis.

• Following mitosis, the cytoplasm divides, separating the two daughter cells. Mitosis

Section 8.2 Summary – pages 201 - 210

Interphase: A Busy Time

• Interphase, the busiest phase of the cell cycle, is divided into three parts.

DNA synthesis and replication

Centrioles replicate; cell prepares for

division

Rapid growth and metabolic activity

Interphase

Section 8.2 Summary – pages 201 - 210

Interphase: A Busy Time

• During the first part, the cell grows and protein production is high.

Rapid growth

and metabolic activity

Interphase

Section 8.2 Summary – pages 201 - 210

Interphase: A Busy Time

• In the next part of interphase, the cell copies its chromosomes.

DNA synthesis and replication

Interphase

Section 8.2 Summary – pages 201 - 210

Interphase: A Busy Time

• After the chromosomes have been duplicated, the cell enters another shorter growth period in which mitochondria and other organelles are manufactured and cell parts needed for cell division are assembled.

Centrioles replicate; cell prepares for division

Interphase

Section 8.2 Summary – pages 201 - 210

Prophase: The first phase of mitosis

• During prophase, the chromatin coils to form visible chromosomes.

Spindle fibers

Disappearing nuclear envelope

Doubled chromosome

Section 8.2 Summary – pages 201 - 210

Prophase: The first phase of mitosis

• The two halves of the doubled structure are called sister chromatids.

Sister chromatids

Section 8.2 Summary – pages 201 - 210

Prophase: The first phase of mitosis

• Sister chromatids are held together by a structure called a centromere, which plays a role in chromosome movement during mitosis.

Centromere

Section 8.2 Summary – pages 201 - 210

Metaphase: The second stage of mitosis

• During metaphase, the chromosomes move to the equator of the spindle.

Centromere

Sister chromatids

Section 8.2 Summary – pages 201 - 210

Anaphase: The third phase of mitosis

• During anaphase, the centromeres split and the sister chromatids are pulled apart to opposite poles of the cell.

Section 8.2 Summary – pages 201 - 210

Telophase: The fourth phase of mitosis

• During telophase, two distinct daughter cells are formed. The cells separate as the cell cycle proceeds into the next interphase.

Nuclear envelope reappears

Two daughter cells are formed

Section 8.2 Summary – pages 201 - 210

Mitosis

Section 8.2 Summary – pages 201 - 210

Cytokinesis

• Following telophase, the cell’s cytoplasm divides in a process called cytokinesis.

• Cytokinesis differs between plants and animals.

• Toward the end of telophase in animal cells, the plasma membrane pinches in along the equator.

Section 8.2 Summary – pages 201 - 210

Cytokinesis

• Plant cells have a rigid cell wall, so the plasma membrane does not pinch in.

• A structure known as the cell plate is laid down across the cell’s equator.

• A cell membrane forms around each cell, and new cell walls form on each side of the cell plate until separation is complete.

Section 8.2 Summary – pages 201 - 210

Results of Mitosis

• When mitosis is complete, unicellular organisms remain as single cells.

• In multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function.

Section 8.2 Summary – pages 201 - 210

Results of Mitosis

• Tissues organize in various combinations to form organs that perform more complex roles within the organism.

• Multiple organs that work together form an organ system.

Section 3 Objectives – page 211

Section Objectives

• Describe the role of enzymes in the regulation of the cell cycle.

• Distinguish between the events of a normal cell cycle and the abnormal events that result in cancer.

• Identify ways to potentially reduce the risk of cancer.

Section 8.3 Summary – pages 211 - 213

Normal Control of the Cell Cycle

• The cell cycle is controlled by proteins called cyclins and a set of enzymes that attach to the cyclin and become activated.

• Occasionally, cells lose control of the cell cycle.

Proteins and enzymes control the cell cycle

Section 8.3 Summary – pages 211 - 213

Normal Control of the Cell Cycle

• Cancer is a malignant growth resulting from uncontrolled cell division.

• This uncontrolled dividing of cells can result from the failure to produce certain enzymes, the overproduction of enzymes, or the production of other enzymes at the wrong time.

Section 8.3 Summary – pages 211 - 213

Normal Control of the Cell Cycle

• Enzyme production is directed by genes located on the chromosomes.

• A gene is a segment of DNA that controls the production of a protein.

Section 8.3 Summary – pages 211 - 213

Cancer: A mistake in the Cell Cycle

• Currently, scientists consider cancer to be a result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle.

• Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients.

Section 8.3 Summary – pages 211 - 213

Cancer: A mistake in the Cell Cycle

• In later stages, cancer cells enter the circulatory system and spread throughout the body, a process called metastasis, forming new tumors that disrupt the function of organs, organ systems, and ultimately, the organism.

Section 8.3 Summary – pages 211 - 213

The causes of cancer

• The causes of cancer are difficult to pinpoint because both genetic and environmental factors are involved.

Section 8.3 Summary – pages 211 - 213

The causes of cancer • Environmental

factors, such as cigarette smoke, air and water pollution, and exposure to ultraviolet radiation from the sun, are all known to damage the genes that control the cell cycle.

Cancer

• Uncontrolled cell

division

• Results from failure

to produce certain

enzymes

• Env. Factors can

trigger damaged

genes into action.

• may be caused by

• Genes

• env. Factors

– Cigarettes

– Pollution

– UV light

– viruses.

• cancer- determined by

where they live more than

genetics

Cancer • 2nd leading cause of

death in U.S.

• Can affect any tissue

of the body

• U.S.-main ones-lung

• Colon

• Breast

• prostate

• - diet-

• low in fat

• & high in fiber

• Fruits, veggies, grain,

and some vitamins &

minerals may prevent

• high fat linked to;

• colon, breast, prostate

cancers

Cancer

• Tumor-Cancerous cells

• form masses of

tissue

• deprive normal

cells of nutrients.

Metastasis

• Final stages of cancer-

• cancer cells enter the

circulatory system &

spread throughout the

body forming new

tumors.

Melanoma • A malignant form of

skin cancer

• most caused by sun

• develops on face or

neck

• 4 Identifying traits

– Asymmetry

– Border

– Color

– Diameter

Basal Cell

Carcinoma

• carcinomas-

• 2nd most common

type of skin cancer. Relatively harmless/removed easily

• can become

squamous cell

• Grows rapidly & spreads

• chemotherapy & radiation therapy used

Section 8.3 Summary – pages 211 - 213

The causes of cancer

• Cancer may also be caused by viral infections that damage the genes.

Section 8.3 Summary – pages 211 - 213

Cancer prevention

• Physicians and dietary experts agree that diets low in fat and high in fiber content can reduce the risk of many kinds of cancer.

• Vitamins and minerals may also help prevent cancer.

Section 8.3 Summary – pages 211 - 213

Cancer prevention

• In addition to diet, other healthy choices such as daily exercise and not using tobacco also are known to reduce the risk of cancer.

Chapter Summary – 8.1

• Osmosis is the diffusion of water through a selectively permeable membrane.

Cellular Transport

• Passive transport moves a substance with the concentration gradient and requires no energy from the cell.

Chapter Summary – 8.1

• Active transport moves materials against the concentration gradient and requires energy to overcome the flow of materials opposite the concentration gradient.

Cellular Transport

• Large particles may enter a cell by endocytosis and leave by exocytosis.

Chapter Summary – 8.2

• Cell size is limited largely by the diffusion rate of materials into and out of the cell, the amount of DNA available to program the cell’s metabolism, and the cell’s surface area-to-volume ratio.

Cell Growth and Reproduction

• The life cycle of a cell is divided into two general periods: a period of active growth and metabolism known as interphase, and a period that leads to cell division known as mitosis.

Chapter Summary – 8.2

• Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase.

Cell Growth and Reproduction

• The cells of most multicellular organisms are organized into tissues, organs, and organ systems.

Chapter Summary – 8.3

• The cell cycle is controlled by key enzymes that are produced at specific points in the cell cycle.

Control of the Cell Cycle

• Cancer is caused by genetic and environmental factors that change the genes that control the cell cycle.