Lesson B1–1



PROCESSES WITHIN THE

PLANT CELLS

Student Learning Objectives. Instruction in this lesson should result in students achieving the following objectives:

1 Describe a plant cell’s components and their function.

2 Describe the structure and function of the nucleus.

3 Describe the structure of DNA.

4 Explain protein synthesis.

5 Explain the steps involved in cellular replication.

6 Explain diffusion.

7 Explain osmosis and osmotic potential.

Anticipated Problem: What are the components of a plant cell and what do they do?

I. Plant cells are made up of cell walls, membranes, cytoplasm, and a variety of organelles.

A. The cell wall is a protective layer made of cellulose which surrounds the cell.

B. The cell membrane is a thin film comprised of two fatty layers that surrounds the cell and regulates the movement of material into and out of the cell.

C. Cytoplasm is the semi-fluid inside the cell membrane that surrounds the organelles.

D. Organelles are small structures inside the cell which carry out the physiological processes of the organism. These are the plant’s organelles and their functions:

1. Chloroplasts, membranes filled with chlorophyll, are the site of photosynthesis.

2. Chromosomes are found inside the nucleus and are made of DNA. The site of the

genetic blueprint of the organism, chromosomes direct all functions of the cell,

including protein synthesis.

3. The endoplasmic reticulum is a system of tubes that moves compounds through the

cell to the ribosomes for protein synthesis.

4. The Golgi apparatus processes, packages, and transports compounds through the

cell.

5. Mitochondria are the site of cellular respiration.

6. The nucleus contains the chromosomes. It is surrounded by a membrane that allows

the materials needed for protein synthesis to pass through.

7. Ribosomes assemble amino acids into proteins.

8. The vacuole is a large storage compartment filled mostly with water.

Anticipated Problem: What is the structure and function of the nucleus?

II. The nucleus is a porous membrane surrounding chromosomes.

A. The membrane allows the passage of fluid carrying chemical messages between the

cytoplasm and the nucleus.

B. Chromosomes are made of chromatin. Chromatin is long strands ofDNAtightly coiled

around protein. A section of this DNA strand codes for a specific protein to be made.

This functional section of DNA is called a gene. Chromosomes exist in pairs, one from

each parent.

Anticipated Problem: What is the structure of DNA?

III. DNA stands for DeoxyriboNucleic Acid. It exists as a double-stranded spiral called a double helix. It looks like a twisted ladder. The steps of the ladder are made of chemicals called nucleotides. The nucleotides are made from: a nitrogen base, a sugar (deoxyribose), and a phosphate group. There are only four possible nitrogen bases:

A. Sugar (deoxyribose)

B. Phosphate group

C. Nitrogen bases (only four possible)

1. Adenine (A)

2. Thymine (T)

3. Guanine (G)

4. Cytosine (C)

D. These base pairs will only match up A with T and G with C across the DNA strand.

E. Following along the strand, the bases are looked at in groups of three called codons. Specific codons signal the formation of a specific amino acid.

Anticipated Problem: How are proteins synthesized in the cell?

IV. There are two basic steps in protein synthesis, transcription and translation.

A. Transcription takes place in the nucleus and involves the following steps:

1. The DNA strand opens up or unzips.

2. Messenger RNA (mRNA) duplicates the sequence of bases from the DNA strand,

substituting uracil for thymine.

3. mRNA passes through the nuclear membrane and endoplasmic reticulum to the

ribosome.

B. Translation takes place in the ribosome. This concludes with the formation of a specific protein.

1. Transfer RNA (tRNA) reads the sequence of codons on the mRNA.

2. tRNA assembles the amino acids coded from the DNA.

3. The amino acids are chemically bound together to form the protein.

Anticipated Problem: What are the steps in cellular replication?

V. The survival of an organism depends on its ability to accurately copy DNA before the cell divides. This occurs as the nucleus divides. After the DNA replicates itself, the cell divides. The process of nucleus division is called mitosis, and it involves four phases. After mitosis, a fifth stage, cytokinesis, takes place to complete cell division. These are the five steps in cell division, with the first four making up mitosis:

A. Prophase: During this phase, the nuclear membrane begins to break down, spindle

fibers appear at each end of the cell, and chromosomes become visible as paired bundles.

B. Metaphase: During this phase, spindle fibers attach to the chromosomes as they group

together.

C. Anaphase: During this phase, the chromosomes divide and separate, moving to opposite ends of the cell.

D. Telophase: During this phase, new nuclear membranes are formed around the groups of chromosomes, the spindle fibers disappear, and the chromosomes uncoil.

E. Cytokinesis: In this final phase, the organelles move to the new nuclei and the cell completes division by forming a plate between the two new complete cells.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 6

Anticipated Problem: What is diffusion and how does it occur?

VI. Because the environment inside the cell is very different from the environment outside the cell, the cell restricts the movement of material into and out of it. This is accomplished through the process of diffusion.

A. The cell membrane acts as a filter, letting some molecules pass through and keeping

others out. This characteristic is referred to as selective permeability. Diffusion involves

the passage of molecules through this semi-permeable membrane.

B. During diffusion, molecules move from areas of high concentration to areas of low concentration, as long as they can pass through the membrane. They will continue to move until they reach a state of equilibrium on both sides of the membrane.

Anticipated Problem: What is osmosis and how does it occur? What is osmotic potential?

VII. Osmosis is the phenomenon where water molecules move from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water across a differentially permeable membrane.

A. If a cell is placed in a solution with a higher concentration of dissolved chemicals than it has inside itself, an imbalance exists. The solution inside the cell has fewer dissolved

chemicals than the solution outside the cell. The chemicals outside the cell will move

into the cell, as long as they can move through the cell membrane, in order to form a

state of equilibrium. If the dissolved chemical cannot get into the cell, water will move

out of the cell in order to achieve this equilibrium. Likewise, if a cell contains more dissolved chemicals than its external environment and the molecules cannot exit the cell,

the cell will take in water to dilute this chemical concentration. This concept is called

osmosis.

B. The level of dissolved chemical in a cell affects the amount of water the cell will absorb. The greater the concentration of dissolved chemicals in the cell, the more water the cell will absorb. A measurable physical force is demonstrated in this situation. The force of the cell to absorb water in order to reach equilibrium with its environment is osmotic potential, or osmotic pressure. If the environment exerts more osmotic potential than the cell, the cell will lose water.

PROCESSES WITHIN THE PLANT CELLS

Part One: Matching

Instructions: Match the word with the correct definition.

a. Cell wall e. Chloroplast i. Nucleus

b. Cell membrane f. Chromosome j. Ribosome

c. Cytoplasm g. Mitochondria k. Vacuole

d. Organelles h. Endoplasmic reticulum l. Golgi apparatus

_______1. A large storage compartment filled mostly with water

_______2. Found inside the nucleus; made of DNA

_______3. A protective layer made of cellulose which surrounds the cell

_______4. A system of tubes which move compounds through the cell

_______5. Small structures inside the cell which carry out physiological processes

_______6. Assemble amino acids into proteins

_______7. A thin film comprised of two fatty layers that surrounds the cell

_______8. Processes, packages, and transports compounds through the cell

_______9. The site of photosynthesis

______10. The site of cellular respiration

______11. The semi-fluid inside the cell that surrounds the organelles

______12. Contains the chromosomes

Part Two: Fill in the Blank

Instructions: Complete the following statements.

1. DNA is made up of three basic components, the nitrogen bases, _____________________, and ________________ ________________.

2. The strand of DNA that functions to code for a specific protein is called a ______________.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 10

3. The four possible nitrogen bases that make up DNA are: ____________________, ____________________, ____________________, and ____________________.

4. ____________________ is long strands of DNA tightly coiled around a protein to form a chromosome.

5. Reading along a DNA strand, the nitrogen bases are looked at in groups of three called _______________.

Part Three: Multiple Choice

Instructions: Circle the letter of the correct answer.

_______1. The process of nucleus division that involves five phases

a. Meiosis

b. Mitosis

c. Miata

d. Mycosis

_______2. During this phase, spindle fibers attach to the chromosomes as they group together.

a. Prophase

b. Metaphase

c. Anaphase

d. Telophase

_______3. During this phase, the chromosomes divide and separate, moving to opposite ends of the cell.

a. Cytokinesis

b. Metaphase

c. Anaphase

d. Telophase

_______4. During this phase, the nuclear membrane begins to break down, spindle fibers appear at each end of the cell, and chromosomes become visible as paired bundles.

a. Prophase

b. Metaphase

c. Anaphase

d. Telophase

_______5. In the final phase of cell division, the organelles move to the new nuclei, and the cell completes division by forming a plate between the two new complete cells.

a. Cytokinesis

b. Metaphase

c. Anaphase

d. Telophase

_______6. During this phase, new nuclear membranes are formed around the groups of chromosomes, the spindle fibers disappear, and the chromosomes uncoil.

a. Prophase

b. Metaphase

c. Anaphase

d. Telophase

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 11

_______7. This involves the passage of molecules through a semi-permeable membrane from an area of high concentration to an area of low concentration.

a. Permeability

b. Solute potential

c. Osmosis

d. Diffusion

_______8. This is the phenomenon in which water molecules move from an area of high concentration to an area

of low concentration.

a. Permeability

b. Solute potential

c. Osmosis

d. Diffusion

_______9. In the DNA strand, the nitrogen base represented by the letter “A” will always pair up with which other nitrogen base?

a. U

b. G

c. T

d. C

______10. In the DNA strand, the nitrogen base represented by the letter “C” will always pair up with which other nitrogen base?

a. A

b. G

c. T

d. U

Part Four: Short Answer

Instructions: Answer the following statements.

There are two basic steps in protein synthesis, transcription and translation.

1. Explain the process of transcription.

2. Explain the process of translation.

3. Explain the concept of osmotic potential.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 12

Assessment

TS–A

Technical Supplement

PROCESSES WITHIN THE PLANT CELLS

It is important to know the parts of a cell, because this provides a basic vocabulary with

which to discuss physiological processes. When studying photosynthesis, for example, it

is helpful to know what a chloroplast is and where it is found. Likewise, when looking at

protein synthesis, it is good to know the architecture of the cell involving this complex

process. Diffusion and osmosis are concepts which help to explain processes including germination, plant/soil water relations, transpiration, nutrient uptake, pesticide absorption, turgor, drought response, and stomata function, to name a few. Understanding diffusion and osmosis, students are better able to explain the phenomenon observed in nature. A knowledge of how the cell functions is important to people doing research in biotechnology. When we identify a specific trait in an organism, we are really identifying proteins that perform some desired function. By manipulating an organism’s DNA, we make changes to the protein synthesis pathway. The cell codes for new proteins. Understanding this process gives students a better appreciation of the objectives and challenges of biotechnology. When we change some function within the cell, we are able to create unique and useful products for agriculture. We have created plants that produce their own pesticide, plants that are able to withstand certain pesticide applications, and still others that can produce enhanced levels of protein. We have manipulated bacteria to produce human insulin and improved the microorganisms which produce cheese. All of these advances in technology started with an understanding of the cell.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 33

What are the components of a plant cell and what do they do?

All organisms are made up of cells. These units of life are able to reproduce, and cells can only come from existing cells. All basic functions of life take place inside the cell. Plant cells are made up of cell walls, membranes, cytoplasm, and a variety of organelles. Following is a list of these plant cell components and their function:

A. The cell wall is a protective layer made of cellulose which surrounds the cell.

B. The cell membrane is a thin film comprised of two fatty layers that surrounds the

cell and regulates the movement of material into and out of the cell.

C. Cytoplasm is the semi-fluid inside the cell membrane which surrounds the

organelles.

D. Organelles are small structures inside the cell which carry out the physiological

processes of the organism. These are the plant’s organelles and their function:

1. Chloroplasts, membranes filled with chlorophyll, are the site of photosynthesis.

2. Chromosomes are found inside the nucleus and are made of DNA. Chromosomes

are the site of the genetic blueprint of the organism, and they direct all

functions of the cell including protein synthesis.

3. The endoplasmic reticulum is a system of tubes which moves compounds

through the cell to the ribosomes for protein synthesis.

4. The Golgi apparatus processes, packages, and transports compounds

through the cell.

5. Mitochondria are the site of cellular respiration.

6. The nucleus contains the chromosomes. It is surrounded by a membrane

that allows the movement of materials needed for protein synthesis to pass

through.

7. Ribosomes assemble amino acids into proteins.

8. The vacuole is a large storage compartment filled mostly with water.

It takes a continual flow of energy for a cell to remain intact and functional. In the case of

plants, this energy is provided by the chloroplast during photosynthesis. This energy is

utilized by the other cell components after it is converted by the mitochondria during respiration. The cell components work together to bring life and function to the cell and,

subsequently, to the whole plant.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 34

What is the structure and function of the nucleus?

The nucleus is important because it stores the genetic information that directs cell function. It also expresses the heredity of the plant. Each cell contains a complete copy of that organism’s genetic code. The function of the nucleus is regulated by its simple structure. The nucleus is a porous membrane surrounding chromosomes.

A. The membrane allows the passage of fluid carrying chemical messages between

the cytoplasm and the nucleus.

B. Chromosomes are made of chromatin. Chromatin is long strands of DNA tightly

coiled around protein. A section of this DNA strand codes for a specific protein to

be made. This functional section of DNA is called a gene. Chromosomes exist in

pairs, one from each parent.

What is the structure of DNA?

DNAstands for DeoxyriboNucleic Acid. It exists as a double-stranded spiral called a double helix. It looks like a twisted ladder. The steps of the ladder are made of chemicals called nucleotides. The nucleotides are made from: a nitrogen base, a sugar (deoxyribose), and a phosphate group. There are only four possible nitrogen bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). These base pairs will only match up A with T and G with C across the DNA strand. Following along the strand, the bases are looked at in groups of three called codons, such as ATG. Specific codons signal the selection of a specific amino acid. In the example ATG, the amino acid tyrosine is selected. It is the combination of these amino acids that form protein molecules.

How are proteins synthesized in the cell?

The expression of a gene is the production of a protein. These proteins are synthesized

within the cell based on the instructions found in the DNA. There are two basic steps in

protein synthesis, transcription and translation. Transcription takes place in the nucleus

and involves the following steps:

1. The DNA strand opens up or unzips.

2. Messenger RNA (mRNA) finds the start codon and duplicates the sequence of

bases from the DNA strand, substituting uracil for thymine, ending at a stop

codon. The mRNA copies A as U, T as A, G as C, and C as G.

3. mRNA passes through the nuclear membrane and endoplasmic reticulum to the

ribosome.

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Translation takes place in the ribosome. Transfer RNA will assemble the various amino

acids into the desired protein. This construction is based on the code or blueprint it reads

from the mRNA. Translation involves the following steps.

1. Transfer RNA (tRNA) reads the sequence of codons on the mRNA.

2. tRNA assembles the amino acids coded for by the DNA.

3. The amino acids are chemically bound together to form the protein.

What are the steps in cellular replication?

The survival of an organism depends on its ability to accurately copy DNA before cell

division. This occurs as the nucleus divides. After the DNA replicates itself, the cell

divides. The process of nucleus division is called mitosis, and it involves four phases. After mitosis, a fifth stage, called cytokinesis, takes place to complete cell division. These are the five steps in cell division, with the first four making up mitosis:

A. Prophase: During this phase, the nuclear membrane begins to break down, spindle

fibers appear at each end of the cell, and chromosomes become visible as paired

bundles.

B. Metaphase: During this phase, spindle fibers attach to the chromosomes as they

group together.

C. Anaphase: During this phase, the chromosomes divide and separate, moving to

opposite ends of the cell.

D. Telophase: During this phase, new nuclear membranes are formed around the

groups of chromosomes, the spindle fibers disappear, and the chromosomes uncoil.

E. Cytokinesis: In this final phase, the organelles move to the new nuclei and the cell

completes division by forming a plate between the two new complete cells.

What is diffusion and how does it occur?

Because the environment inside the cell is very different from the environment outside

the cell, the cell restricts the movement of material into and out of it. This is accomplished through the process of diffusion. The cell membrane acts as a filter, letting some molecules pass through and keeping others out. This characteristic is referred to as selective permeability. Diffusion involves the passage of molecules through this semi-permeable membrane. During diffusion, molecules move from areas of high concentration to areas of low concentration, as long as they can pass through the membrane. They will continue to move until they reach a state of equilibrium on both sides of the membrane.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 36

What is osmosis and how does it occur? What is osmotic potential?

Osmosis is the phenomenon in which water molecules move from an area of high concentration to an area of low concentration. Osmosis is the diffusion of water across a differentially permeable membrane. If a cell is placed in a solution with a higher concentration of dissolved chemicals than it has inside itself, an imbalance exists. The solution inside the cell has fewer dissolved chemicals than the solution outside the cell. The chemicals outside the cell will move into the cell, as long as they can move through the cell membrane, in order to form a state of equilibrium. If the dissolved chemical cannot get into the cell, water will move out of the cell in order to achieve this equilibrium. Likewise, if a cell contains more dissolved chemicals than its external environment, and the molecules cannot exit the cell, the cell will take in water to dilute this chemical concentration. This concept is called osmosis. The level of dissolved chemical in a cell affects the amount of water the cell will absorb. The greater the concentration of dissolved chemicals in the cell, the more water the cell will absorb. There is a measurable physical force that is demonstrated in this situation. The force the cell exerts to absorb water in order to reach equilibrium with its environment is osmotic potential, or osmotic pressure. If the environment exerts more osmotic potential than the cell, the cell will lose water as in transpiration.

Illinois Biological Science Applications in Agriculture Lesson B1–1 • Page 37

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