Science 7Module

Cell Structure and Function

Smiling Grass Cell

Philippine Normal UniversityTaft Ave., Manila

College of EducationDepartment of field Study and Student Teaching

Certificate of Teaching Program(CTP)

About the Cover

(Photo not mine, credits to the owner)A cross section of the leaf of marram grass Ammophila arenaria, a species of dune grass that’s primarily responsible for trapping wind­blown sand and building the dune systems around our coast. Marram grass survives by rolling up its leaves during long periods of drought, minimizing water loss. This cross section of a partially rolled leaf has been stained with fluorescent dyes to light up different cell

types within the leaf, with the outside surface of the leaf at the bottom of the picture (smooth, curved surface) and the inner convoluted surface at the top.(http://beyondthehumaneye.blogspot.com/2009/06/dune­builder.html)

Copyright Page

Science 7ModuleCell Structure and Function

byJohn Daniel P. Gumban

toDr. Lenard A. Tabaranza

October 2013

ModuleCell Structure and Function

What this module is about

This module will help you gain knowledge about cell: the basic unit of all living matter. It is the unit of structure and function of which all plants and animals are

composed. The cell is the smallest unit in the living organism that is capable of integrating the essential life processes. The cell is the key to biology because it is at this level that life truly springs. As you read this, you will learn more about the activities of the cell, the structures and the material of life that fills them. Later on, you will discover what a living matter is made of.

This module has the following lessons: Lesson 1 ­ Cell Theory Lesson 2 ­ Cell: The Basis of Life Lesson 3 ­ Cell Types

What are you expected to learn

After going this module, you are expected to: Identify the different parts of the cell; Differentiate plant cells from animal cell; Differentiate unicellular organisms from multicellular organisms; Differentiate prokaryotic from eukaryotic cells; Appreciate cell as a highly organized structure.

How to learn from this module

I know you want to start to learn about cells. So you must follow these stepsand instructions to be able to achieve the objectives of this module.

Read and follow the instructions carefully. Answer the pretest before you start the lesson. Take note and record point for clarification. Try to achieve at least 75% level of proficiency in the tests. Work diligently and honestly. Answer the protest.

What to do before (Pretest)To start off, you have to answer the pre­test for you to measure how much

you know about the topic. You can start now.

There are 20 questions. Each question has ONLY ONE CORRECT ANSWER. Choose the one you believe to be best. Each question is worth 2 points. Read each question fully and carefully. Take your time. GOOD LUCK!

1. A cell is observed to contain a nucleus, mitochondria and chloroplasts. From this information you can conclude that the cell is:

a. a plant cell c. a bacteria cellb. an animal cell d. a prokaryotic cell

2. A cell that lacks a nucleus and membrane bound organelles is known as a (an) ______________ cell.

a. plant c. eukaryoteb. animal d. prokaryote

3. A cell with relatively few energy needs will probably have a relatively small number of ________________.

a. ribosomes c. mitochondriab. lysosomes d. chromosomes

4. Digestive enzymes or hydrolytic enzymes are terms associated with _________.a. ribosomes c. golgi apparatusb. lysosomes d. smooth endoplasmic reticulum

5. In which of the following items would you expect to find cells?a. strawberry c. silver dollarb. eyeglasses d. plastic flower

6. Organisms whose cells do not have a nucleus are called _______________.a. plants c. eukaryotesb. organelles d. prokaryotes

7. Plant cells often have a box­like shape because of the ________________.a. nucleus c. cytoplasmb. cell wall d. cell membrane

8. The site of ATP production and the site of photosynthesis are the _______________ and _________________.

a. ribosomes and vacuoles c. mitochondria and chloroplastb. chloroplasts and lysosome d. Golgi complex and chloroplast

9. What is the outermost boundary of an animal cell?a. the cell wall c. the cell membraneb. the cytoplasm d. the nuclear envelope

10. What site regulates what goes in and out of the cell?a. cell wall c. cell membraneb. vacuole d. nuclear membrane

11. What type of cell has these characteristics: contains DNA but no nucleus, contains flagella, ribosomes, cytoplasm, and a cell membrane.

a. plant c. animalb. fungi d. bacteria

12. Where is the site of protein synthesis?a. nucleus c. ribosomeb. lysosome d. mitochondria

13. Which is the “brain” of the cell?a. nucleus c. golgi bodiesb. chloroplast d. mitochondria

14. Which of the following forms of life is not eukaryotic?a. a bacteria cell c. a plant cell like gumamelab. protist such as amoeba d. a human cell such as Red Blood Cell

15. Which of the following is found in the nucleus?a. vacuoles c. mitochondriab. chloroplasts d. chromosomes

c.16. Which of the following is not true of chloroplasts?

a. They synthesize sugar c. They are only found in plants.b. They contain pigments d. They appear green because of chlorophyll

17. Which of the following organelles transports materials inside the cell?a. lysosome c. mitochondriab. chloroplast d. endoplasmic reticulum

18. Which of the following statements is always true?a. All cells have a cell wall. c. All cells contain chloroplast.b. All cells contain nucleus. d. All cells have cell membrane.

19. Which of the following structures are common to both eukaryotic and prokaryotic cells?a. nucleus c. both b and cb. ribosomes d. cell membrane

20. Which organelle has no membrane?a. vacuole c. ribosomeb. lysosome d. chloroplast

Lesson 1. Cell TheoryThe cell theory, or cell doctrine, states that all organisms are composed of

similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden and Schwann and has remained as the foundation of modern biology. The idea predates other great paradigms of biology including Darwin’s theory of evolution (1859), Mendel’s laws of inheritance (1865), and the establishment of comparative biochemistry (1940).

Fact FileThe average human being is composed of around 100 Trillion individual cells. It would take as many as 50 cells to cover the area of a dot on the letter “i”.

First Cells Seen in Cork“I took a good clear piece of Cork and with a Pen­knife sharpen’d as keen as a razor …

cut off … an exceeding thin piece of it, and placing it on a balck object Plate … and casting the light on it with a deep planoconvex Glass, I could exceedingly plainly perceive it to be all perforated and porous … these pores, or cells, were not very deep, but consisted of a great many little Boxes, separated out of one continued long pore by certain Diaphragms … Nor is this kind of texture peculiar to Cork only; for upon examination with my Microscope, I have found that the pith of an Elder, or almost any other Tree, the inner pul or pith of the Cany hollow stalks of several other Vegetables: as of Fennel, Carrets, Daucus, Bur­docks, Teasels, Fearn … & c. have so much kind of Schematisme, as I have lately shown that of Cork.”

­ Robert Hooke (first report on the existence of cell, 1665) from Microphagia

While the invention of the telescope made the Cosmosaccessible to human observation, the microscope opened up smallerworlds, showing what living forms were composed of. The cell wasfirst discovered and named by Robert Hooke in 1665. He remarkedthat it looked strangely similar to cellula or small rooms which monksinhabited, thus deriving the name. However what Hooke actually sawwas the dead cell walls of plant cells (cork) as it appeared under themicroscope. Hooke’s description of these cells was published inMicrographia. The cell walls observed by Hooke gave no indication ofthe nucleus and other organelles found in most living cells.

Figure 1.1 The cellsobserved by Hook in thehoneycomb structure ofa cork tissue

Using handcrafted microscopes, Anton van Leeuwenhoek was the first person to observe and describe single celled organisms, which he originally referred to as animalcules (which we now refer to as microorganisms). He was also the first to record and observe muscle fibres, bacteria, spermatozoa and blood flow in capillaries (small blood vessels).

Fact FileIn 1681, Anton van Leeuwenhoek examined his own stool samples during times of diarrhea. In his runny stool, he found little animals. Leeuwenhoek described Giardia being a slow moving animal, but able to make quick motions with their “paws.” Today, we know this is a helical motion that is caused by flagella.

Formulation of Cell TheoryIn 1838, Theodor Schwann and Matthias Schleiden were enjoying after­dinner coffee and

talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann’s lab to look at his slides. Schwann published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of acknowledgments of anyone else’s contribution, including that of Schleiden (1838).

These discoveries of Schleiden and Schwann introduced the cell theory. This theory states that:

1. All living things are made up of one or more cells.2. The cell is the fundamental, structural and functional unit of all living organisms.

In 1855, third statement on the cell theory was added by Rudolf Virchow. It states that:

3. All living cells come from pre­existing cells, by division.

This ability of cells to divide and form new cells is the reason for the reproduction and growth of all organisms.

The modern principles of the Cell Theory include the following:1. All living things are made up of one or more cells.2. The cell is the fundamental, structural and functional unit of all living organisms.3. All living cells come from pre­existing cells, by division.4. The activity of an organism is the total activity of the independent cells of the organism.5. All energy flow of life occurs within the cell.6. The cells contain hereditary information and is passed from one to another during cell

division.7. The chemical composition of cell are basically the same in organisms of similar species.

Table 1.1 Landmarks in the Study of Cell Biology

1595 Hans and Zacharias Jansen credited with 1st compound microscope.

1626 Francesco Redi postulated that living things do not arise from spontaneous generation.

1655 Robert Hooke described ‘cells’ in cork.

1674 Anton Van Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later.

1833 Robert Brown described the cell nucleus in cells of the orchid.

1840 Albrecht von Roelliker realized that sperm cells and egg cell are also cells.

1856 Nathanael Pringsheim observed how a sperm cell penetrated an egg cell.

1858 Rudolf Virchow (physician, pathologist and anthropologist) expounds his famousconclusion: “omnis cellula e cellula”, that is “cells develop only from existing cells”(cells come from pre­existing cells)

1857 Albert von Kölliker described mitochondria.

1869 Johannes Friedrich Miescher isolated DNA for the first time.

1879 Walther Flemming described chromosome behavior during mitosis.

1833 Germ cell are haploid, chromosome theory of heredity.

1898 Golgi described the golgi apparatus.

1926 Theodor Svedberg developed the first analytical ultracentrifuge.

1938 Peter Behrens used differential centrifugation to separate nuclei from cytoplasm.

1939 Siemens produced the first commercial transmission electron microscope,

1941 Albert Coons used fluorescent labeled antibodies to detect cellular antigens.

1952 George Otto Gey and co­workers established a continuous human cell line.

1953 Francis Crick, Maurice Wilkins and James Watson proposed structure of DNAdouble­helix.

1955 Harry Eagle systematically defined the nutritional needs of animal cells in culture.

1957 Matthew Meselson, Franklin Stahl and Jerome Vinograd developed density gradientcentrifugation in cesium chloride solutions for separating nucleic acids.

1965 RG Ham introduced a defined serum­free medium. Cambridge Instruments producedthe first commercial scanning electron microscope.

1976 Rizzino Sato and colleagues publish papers showing that different cell lines requiredifferent mixtures of hormones and growth factors in serum­free media.

1981 Transgenic mice and fruit flies are produced. Mouse embryonic stem cell lineestablished.

1987 First knockout mouse created.

1998 Mice are cloned from somatic cells.

2000 Human genome DNA sequence draft.

2001 Cell cycle regulation (cyclins).

2002 Mouse genome sequenced.

2004 Rat genome sequenced.

2006 Andrew Fire and Craig Mello described method of RNA interference (RNAi) withsingle­stranded RNA.

Prior to 1931 when the first electron microscope was developed, magnification of microscopes was limited to about 2000 times. The small cell structures did not show up well or remained invisible. The electron microscope not only showed more detail of previously known parts of the cell but also revealed new parts. Cells and cell structures can now be examined at magnifications of up to 500 000 times and more.

Fact FileThe shape and appearance of a cell depends on what job it does. Cells consist of jelly­like cytoplasm, surrounded by a membrane. Nutrients pass through this membrane and substances produced by the cell leave.

What you will doActivity 1.1

The Street SweepersThe air we breathe is filled with dust, smoke, and even small bacteria.

How come all these materials do not accumulate in the lungs and clog theirpassageways?

What you will doSelf Test 1.1

Answer the following questions briefly.

1. What contributions did van Leeuwenhoek, Hook, Schleiden, Schwann, and Virchow make to the development of the cell theory?

2. What role did the invention of the microscope play in the development of the cell theory?

Lesson 2. Cell: The Basis of Life

Have you tried check leaves and observe its surface? Have you tried to exam the wings of insects? Have you ever observed the skin of the onion? Such curiosity led early scientist to examine living things in the hope of getting a better view of their structure. Little by little, they discovered that all living things are made of cells. Cell is the fundamental, structural and functional unit of all living organisms such as the birds you watch, the cork trees and so on are made of living cells.

Figure 2.1 All living organisms are composed of one or more cells.http://www.deshow.net/animal/bing­animal­wallpaper­846.html

Fact FileCells need food, oxygen and a watery environment in order to survive.Food and water are supplied by the blood and other body fluids, whichalso carry away wastes. Blood also contains all of the food substancesand chemicals needed by the cell.

THE STRUCTURE OF THE CELL

Cells have three major parts:1. Nucleus serves as the control center of the cell;2. Cytoplasm is the material between the nucleus and the outer boundary where

organelles are found;3. Cell Membrane serves as the outer boundary of the cell and organelles the

passage of materials to and from the cell.

Cell Membrane

The cell membrane is a thin semi­permeablemembrane that surrounds the cytoplasm of a cell,enclosing its contents. Its function is to protect theintegrity of the interior of the cell by allowing certainsubstances into the cell, while keeping other substancesout. It also serves as a base of attachment for thecytoskeleton in some organisms and the cell wall inothers. Thus the cell membrane also serves to helpsupport the cell and help maintain its shape.

Figure 2.2Cell Membrane

Find OutBreak a chicken egg into a dish, and look at the yolk. How large do you think is it?Estimate its width. Then use a metric ruler to measure the width of your chicken yolk cell. With a hand lens, observe the yolk closely. Other cells that can be seen easily are large fish eggs.

Feedback: Most cells are too small to be seen without the help of a microscope. Luckily, there are a few cells that can be seen with your naked eyes.

Fact FileThe largest cell in human body is the egg cell or ovum, which may befertilized by a sperm cell and grow into a baby.

Cytoplasm StructuresThe cytoplasm consists of all of the contents outside of the nucleus and enclosed within

the cell membrane of a cell. This includes mitochondria, endoplasmic reticulum, ribosome, golgibodies, lysosomes, and vacuole.

Mitochondria are commonly called the “power houses” of the cell. They trap the energy that results when food is broken down. Just as a power plant supplies energy to a business, mitochondria provide energy for the cell. Some types of cells are more active than others, that’s why they can have more mitochondria.

Figure 2.3Mitochondria

Analyze ThisWhy might a muscle cell have more mitochondria than other cells?

Feedback: Muscle cells are always undergoing some type of movement. Muscles are also the ones exposed to strenuous activities like doing some household chores, running, walking, etc.

Endoplasmic reticulum are network of canals extends from the nucleus to the cell membrane and takes up quite a lot of space in some cells. It moves material from one place to

another place inside the cell. There are two regions of the endoplasmic reticulum that differ in both structure and function. One region is called Rough Endoplasmic Reticulum because it has ribosomes attached to the cytoplasmic side of the membrane. The other region is called Smooth Endoplasmic Reticulum because it lacks attached ribosomes. Typically, the smooth endoplasmic reticulum is a tubule network and the rough endoplasmic reticulum is a series of flattened sacs.

Figure 2.4Endoplasmic Reticulum

Ribosomes are the tiny dots you see on the edges of some of the endoplasmic reticulum. Some cells may contain millions of ribosomes. Ribosomes are cell organelles that consist of RNA and proteins. They are responsible for assembling the proteins of the cell. Depending on the protein production level of a particular cell, ribosomes may number in the millions.

Figure 2.5Ribosome

Fact FileCells contain thousands of ribosomes. Ribosomes are organelles that produce amino acids and proteins in the cells. They do this by reading RNA (ribonucleic acid), which is a process called translation. Every second, ribosomes can add 3+ amino acids to a new protein.

In a manufacturing business, products are made, packaged, and moved to loading centers to be carried away. Structures called golgi bodies are responsible for manufacturing, warehousing, and shipping certain cellular products, particularly those from the endoplasmic reticulum (ER). Depending on the type of cell, there can be just a few complexes or there can be hundreds. Cells that specialize in secreting various substances typically have a high number of Golgi bodies. are the packaging and releasing structures of the cell. When something is released, it is given off by the cell.

Figure 2.6Golgi Bodies

Applying a ConceptAn animal cell contains about 10 to 20 golgi bodies, while a plant cell contains several hundreds. Why do you think there is such a difference in the number of these structures in each cell type?

Feedback: The fact that plants produce so many materials (food, oils, resins, etc.), they will be in need of more golgi bodies to store the said materials.

Do you know that cells also produce wastes? In the cytoplasm, structures called lysosomes. Lysosomes are membranous sacs of enzymes. They are made by the endoplasmic reticulum and Golgi bodies. Lysosomes contain various hydrolytic enzymes that are capable of digesting nucleic acid, polysaccharides, fats, and proteins.They are active in recycling the cell's organic material and in the intracellular digestion of macromolecules. In addition, in many organisms, lysosomes are involved in programmed cell death. On the other hand, lysosomes contain chemicals that digest wastes and worn­out/damaged cell parts. When a cell dies, chemicals in the lysosomes act to quickly break down the cell. In a healthy cell, the membrane around the lysosome keeps it from breaking down the cell itself. Plant cells do not have lysosomes. Figure 2.7

Lysosome

Fact FileThere are two ways that a cell can die: necrosis and apoptosis. Necrosis occurs when a cell is damaged by an external force, such as poison, a bodily injury, an infection or getting cut off from the blood supply. Apoptosis, it's when a cell commits suicide. It's sometimes referred to as programmed cell death, and indeed, the process of apoptosis follows a controlled, predictable routine.

Many businesses have warehouses for storing products until they are sold. Vacuoles are storage areas in cells. A membrane­bound vesicle found in the cytoplasm of a cell whose function includes intracellular secretion, excretion, storage, and digestion. It can be found in animal and plant cells, and it can be especially conspicuous in plant cells.

Figure 2.8Vacuole

Analyze ThisIn plant cells, vacuoles are big. In animal cells, vacuoles are small. Why do youthink so?

Feedback: Plants are said to be the producers of food in the environment. They may produce sugar, oil, nectar, etc. They are in need of bigger vacuoles to store such materials.

The Nucleus

The nucleus is a membrane bound structure and act as the “control center” of the cell. The nucleus contains the cell's hereditary information and controls the cell's growth and reproduction. The nucleus is bounded by a double membrane called the nuclear envelope (nuclear membrane). This membrane separates the contents of the nucleus from the cytoplasm. The envelope helps to maintain the shape of the nucleus and assists in regulating the flow of molecules into and out of the nucleus through nuclear pores. The nucleus contains coded instructions for all of the cell’s activities. These coded instructions are stored on special structure called the chromosomes. When a cell is "resting" i.e. not dividing, the chromosomes are organized into long entangled structures called chromatin and not into individual chromosomes as we typically think of them. The nucleus also contains the nucleolus which helps to synthesize ribosomes. The nucleolus contains nucleolar organizers which are parts of chromosomes with the genes for ribosome synthesis on them. Copious amounts of RNA and proteins can be found in the nucleolus as well. The nucleus controls the synthesis of proteins in the cytoplasm through the use of messenger RNA. Messenger RNA is produced in the nucleolus of the cell and travels to the cytoplasm through the pores of the nuclear envelope.

Figure 2.9Parts of Nucleus

Fact FileA typical DNA molecule is so long and thin that if it were the thickness of spaghetti, it would be 5 miles (8km) long.

Figure 2.10Animal Cell

You have just looked at the inner workings of an animal cell. Imagine now that you are taking a microscopic tour through the green plant cell on the side. You will find that some structures in this cell are quite different from the structures in an animal cell. Take note of them. The outer covering of the plant cell is not soft and thin. Instead, it is surrounded by a rigid/tough structure called the cell wall that supports and protects the plant cell. Once you pass through the cell wall, you see the same structures you saw in the animal cell. The dark green bodies you see around you are chloroplasts. Substances inside the chloroplast help a green plant cell trap the sun’s energy and then produce food.

Figure 2.11Plant Cell

Imagine you could take a trip into a tiny bacterial cell. Bacteria and blue­bacteria are quite different from other cells. They have fewer structures than plant or animal cells. However, they carry out all of the life processes that other cells carry out. You can see that a bacterium has a cell wall, a cell membrane, and cytoplasm. The chromosome material (nucleoid), which directs the cell’s activities, floats freely through the cytoplasm. The other structures are lacking.

Figure 2.12Bacterial Cell

Fact FileBacteria are tiny, single­celled organisms. They can measure as little as 0.001 mm across and they can only be seen under a microscope. There are many different sorts of bacteria, and most of them are harmless.

What you will doActivity 2.1

ChallengeMake your own model of a cell at home. Prepare a small package of gulaman and pour it into dish. Put common foods in the gelatin to represent cell structures. You could use lettuce or shredded carrots for endoplasmic reticulum and raisins for mitochondria. Be creative! Unmold your “cell”. And serve it to your family for salad or dessert.

What you will doSelf­test 2.1

Let us see how well you can make a summary of what you know about the cell. Below is a table that lists the names of the cell structure(s). Now, compare animal, plant and bacterial cells by putting a (/) if the structure is present and an (x) if the structure is absent under each column.

Structures Animal Cell Plant Cell Bacterial Cell

1. Cell wall

2. Cell membrane

3. Cytoplasm

4. Mitochondria

5. Ribosomes

6.Endoplasmic Reticulum

7. Golgi bodies

8. Lysosomes

9. Vacuoles

10. Chloroplasts

11. Nucleus

12. Chromosomes

What you will doSelf Test 2.2

A Tale of a Tail

Mr. Gumban’s' class studied the parts of plant and animal cells. The class captured tiny tadpoles in a local stream. Mr. Gumban showed the students how to care for the tadpoles in the classroom. Gradually, as the animals grew, the bodies were changing in shape. Back and front legs grew out. The mouth expanded from a small hole to a large opening capable of swallowing large insects. In addition, the tails started to disappear. Mr. Gumban told the whole class that there would be a bonus question about the tadpoles in the test on animals. For a study clue, she told them to review their notes on cells. What do changes in the body parts of the tadpoles have to do with cells? Figure 2.13

Tadpole

Think critically:

Answer the bonus question:

What cell part makes the tadpole tails disappear? How?

Lesson 3. Cell Types

PROKARYOTES AND EUKARYOTES

Not all organelles described in the previous section are present in all cells. Cells can be grouped into two large categories: prokaryotes (cell without a true nucleus) and eukaryotes (cell with a true nucleus).

ProkaryotesProkaryotes are single­celled organisms that are the earliest and most primitive forms of

life on earth. As organized in the Three Domain System, prokaryotes include bacteria and archaeans. Prokaryotes are able to live and thrive in various types of environments including extreme habitats such as hydrothermal vents, hot springs, swamps, wetlands, and the guts of animals.

Fact FileThe first recorded observation were of the bacteria found in the dental plaque of two old men who never cleaned their teeth.

Prokaryotic Cell StructureProkaryotic cells are not as complex as eukaryotic cells. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell, but is coiled up in a region of the cytoplasm called the nucleoid. Prokaryotes do not have membrane­bound organelles like mitochondria and endoplasmic reticulum. They do not possess lysosomes, vacuoles, and Golgi bodies. Their ribosomes are small. Chlorophyll, when present, is not contained in chloroplasts.

Figure 3.1 Examples of Prokaryotes. From left to right: lactobacillus, E. coli and salmonella.

EukaryotesEukaryotes include animals, plants, fungi and protists. Typically, eukaryotic cells are more complex and much larger than prokaryotic cells. On average, prokaryotic cells are about 10 times smaller in diameter than eukaryotic cells. Eukaryotes have well­defined nuclear membrane and distinct nucleolus. Membrane­bound organelles are found in eukaryotes, such as Golgi bodies and mitochondria.

Plant and Animal CellsThe second cell grouping is Plants versus Animal cells. Both of these cell types are

eukaryotes. This means they have a lot of organelles in common. One organelle they don’t have in common is chloroplasts, which only plants have. Another organelle difference is the vacuoles. In animal cells the vacuoles are small and plenty. In the plant cells, there is a large central vacuole that occupies over 50% of the plant cell’s volume. This vacuole is filled with water and nutrients under pressure. The pressure helps maintain the plant cell’s rigid shape. The rigid shape results in plant cells looking rectangular as compared to the round like animal cells. While both cell types have cell membranes, the plant cell’s rigidity is further maintained by an additional cell wall outside the membrane.

Figure 3.2 Eukaryotic Organisms

Fact FileDNA strands look like a twisted ladder. Sections of DNA are called genes. All the instructions for growing a new human being are coded into the DNA molecule.

Table 3.1 Comparison of prokaryotic and Eukaryotic Cells.

Cell Structure Prokaryotic Cell Eukaryotic Cell

Cell membrane present present

Nuclear membrane absent present

Membrane­bound organelles absent present

Ribosomes small large

Chlorophyll when present are not found in chloroplasts

found in chloroplasts

Mitochondria absent present

Chromosomes single loop of circular DNA multiple double­helix

Fact FileChromosomes are tiny threads that are present in all cells apart from red blood cells. They contain all the information for an entire person to develop. There are 46 chromosomes in each cell. They come in 22 pairs, plus another special pair that determine the person’s sex.

What you will doSelf Test 3.1

Answer the following questions:

1. Chloroplasts are found in which type of cell?

2. What do you call the broad group of cells that lack membrane bounded organelles?

3. What type of cell (prokaryote or eukaryote) has DNA that floats freely in the cell?

4. Mushroom is a unicellular organism. (True or false)

5. Human is a multicellular organism. (True or false)

Let’s Summarize

1. Cells are amazing, variable, beautiful, and functionally superb. A concept of genius, they work alone or in groups with equal ease.

2. Cells are the basic units of life. All living things are made up of one or more cells. Organisms that exist as single cells are called unicellular and organisms that are made up of groups of cells working together are called multicellular.

3. Because all living things are made up of cells, and because we desire to understand ourselves and the other living things around us it makes sense to learn something about cells.

4. All living things are divided into two major groups depending on how their cells are set up. These two groups are the Prokaryotes and the Eukaryotes.

5. The basic structure of plant and animal cell is almost the same except for certain differences. The basic structure of a cell is composed of the following components.

a. Cell Membraneb. Cytoplasmc. Nucleus

However in plants, a rigid "Cell wall" is present outside the cell membrane or plasma membrane.

6. Cell Theory: All living things are composed of cells. Cells are the basic units of structure and function in living things. All cells come from preexisting cells

Whew! At last! You have finished studying the module. But, before you completely exit from this module, let us find out how much you learned from this material.

Post-TestMultiple Choice. Choose the letter of the best answer. Write the chosen letter on a separate sheet of paper.

1. A cell is observed to contain a nucleus, mitochondria and chloroplasts. From this information you can conclude that the cell is:

a. a plant cell c. a bacterial cellb. a animal cell d. a prokaryotic cell

2. A cell that lacks a nucleus and membrane bound organelles is known as a(an) ______________ cell.

a. plant c.eukaryoteb. animal d. prokaryote

3. A cell with relatively few energy needs will probably have a relatively small number ofa. ribosomes c. mitochondriab. lysosomes d. chromosomes

4. Digestive enzymes or hydrolytic enzymes are terms associated witha. ribosomes c. golgi apparatusb. lysosomes d. smooth endoplasmic reticulum

5. In which of the following items would you expect to find cells?a. strawberry c. silver dollarb. eyeglasses d. plastic flower

6. Organisms whose cells do not have a nucleus are calleda. plants c. eukaryotesb. organelles d. prokaryotes

7. Plant cells often have a box­like shape because of thea. nucleus c. cytoplasmsb. cell wall d. cell membrane

8. The site of ATP production and the site of photosynthesis are the _______________ and _________________.

a. ribosomes and vacuoles c. mitochondria and chloroplastsb. chloroplasts and lysosomes d. Golgi complex and chloroplast

9. What is the outermost boundary of an animal cell?a. the cell wall c. the nuclear membraneb. the cytoplasm d. the nuclear envelope

10. What site regulates what goes in and out of the cell?a. cell wall c. cell membraneb. vacuole d. nuclear membrane

11. What type of cell has these characteristics: contains DNA but no nucleus, contains flagella, ribosomes, cytoplasm, and a cell membrane.

a. plant c. animalb. fungi d. bacteria

12. Where is the site of protein synthesis?a. nucleus c. ribosomeb. lysosomes d. mitochondria

13. Which is the “brain” of the cell?a. nucleus c. golgi bodiesb. chlorop[lats d. mitochondria

14. Which of the following forms of life is NOT eukaryotic?a. a bacterial cell c. a plant cell like gumamelab. protist such as amoeba d. a human cell such as red blood cell

15. Which of the following is found in the nucleus?a. vacuole c. mitochondriab. chloroplasts d. chromosomes

16. Which of the following is NOT true of chloroplasts?a. They synthesize sugarb. They contain pigmentsc. They are only found in plantad. They appear green because of chlorophyll

17. Which of the following organelles transports materials inside the cella. lysosome c. mitochondriab. chloroplasts d. endoplasmic reticulum

18. Which of the following statements is always true?a. All cells have a cell wall c. All cells contain chloroplast.b. All cells contain nucleus. d. All cells have a cell membrane.

19. Which of the following structures are common to both eukaryotic and prokaryotic cells?a. nucleus c. both b and cb. ribosomes d. cell membrane

20. Which organelle has no membrane?a. vacuole c. ribosomeb. lysosome d. chloroplast

Key to Answers

Pretest1. c 6. d 11. d 16. c2. d 7. b 12. a 17. a3. d 8. a 13. d 18. d4. c 9. b 14. b 19. c5. a 10. c 15. c 20. c

LESSON 1

Activity 1.1The Street Sweepers

Lining the passageways are special cells that release a mixture of water, carbohydrates, and salts, called mucus. The particles of dust and dirt that are inhaled are trapped in this sticky mucus. Underneath this layer of mucus is another group of specialized cells that have cilia. As the cilia move, they create a sweeping action. This action keeps the most vital passageways in the body clean and open for business.

Self­Test 1.11. Leeuwenhoek: discovered protozoa

Hooke: described “cells” in corkSchleiden & Schwann: proposed cell theoryVirchow: concluded that cells come from preexisting cells

2. The microscope opened up the world of the very small to biologists. It enabled scientists to discover that all living things are made up of cells.

LESSON 2

Self­Test 2.1

Structures Animal Cell Plant Cell Bacterial Cell

1. Cell wall X / /

2. Cell membrane / / /

3. Cytoplasm / / /

4. Mitochondria / / x

5. Ribosomes / / /

6.Endoplasmic Reticulum / / x

7. Golgi bodies / / x

8. Lysosomes / x x

9. Vacuoles / / x

10. Chloroplasts x / x

11. Nucleus / / x

12. Chromosomes / / /

Self­Test 2.2The body parts of the tadpoles change in response to the activity of the cells which is cell division. When cells divide, their number increases. Growth results when cells increase in number.

The tails of the tadpole disappear due to the lysosomal activity. The lysosome, if you will recall, contains powerful chemicals which are used to digest or break down materials

LESSON 3

Activity 3.1Feedback: One­celled organisms may have fewer or different structures from plant or animal cells. However, they carry out all of the life processes (reproduction, digestion, excretion, respiration, etc.) that other cells carry out.

Self­Test 3.11. plant2. prokaryote3. prokaryote4. false5. true

Post­Test1. c 6. b 11. b 16. c2. d 7. a 12. a 17. a3. d 8. c 13. d 18. d4. b 9. c 14. b 19. c5. c 10. d 15. a 20. c

References

Books:

Ahuja M.; (2006). Life Sciences. Gyan Publishing House. pp. 105­109

Chancellor Press (Bounty Books); (2001). Tell Me What?. WS Pacific Publications Inc., Manila,Philippines. pp. 38­71

Chancellor Press (Bounty Books); (2001). Tell Me Where?. WS Pacific Publications Inc., Manila,Philippines. pp. 140­173

Chancellor Press (Bounty Books); (2001). Tell me When?. WS Pacific Publications Inc., Manila,Philippines. pp. 38­71

Lozano, L.; Sandico, P.M.; (2003). Science and Technology for the Future II. Diwa ScholasticPress Inc. pp. 92­104

Module:

Project EASE (Effective Alternative Secondary Education). Biology Module 2. Cell structure andFunction. Bureau of Secondary Education, Department of Education, Pasig City.

Electronic Sources:

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