CHAPTER 2 : CELL STRUCTURE AND CELL ORGANISATION

Textbook

Focus Practise 2.1 (page 22)

1. Why is the use of the electron microscope important in the study of cell biology ?

      Electron microscope enables scientist to see the cellular components of a cell in

greater details.  Some of the organelles can only be seen under an electron microscope.

2. Why is it important to study cellular components and their functions?

Living organisms are made of basic units forming the building blocks of all living organisms.

3. Which organelle is found abundantly in a cell that secretes protein products?

Ribosome, Rough ER, Golgi apparatus.

Ribosomes – synthesis of proteins

Rough ER – transport of protein from one part of the cell to another

Golgi apparatus – processing, packaging and transporting proteins, phospholipids  

                             and glycoproteins

4. Match the following cellular components to their functions.

Cellular component	Function
A.Vacuole	An organelle that contains digestive enzymes ( C )
B.Smooth endoplasmic       reticulum	An organelle that traps light energy during photosynthesis ( D )
C. Lysosome	A fluid-filled sac which contains a complex mixture of sugars, mineral salts, pigments and waste products ( A )
D. Chloroplast	An organelle which is involved in the synthesis of lipids ( B )

Focus Practice 2.2 (page 35)

1. What is the function of contractile vacuoles in Amoeba sp.?

 Contractile vacuoles of unicellular organisms such as Amoeba  sp. help regulate water balance by pumping out excess water that diffuses into the cell.

2. Explain the process of phagocytosis in Amoeba sp.

 The process of phagocytosis involves;

·         Amoeba sp. approaches the food particles

·         Two pseudopodium extend out and enclose the food particles

·         The food particles are packaged in a food vacuole, which fuses with a lysosome containing hydrochloric enzymes called lysozyme

·         The food particles are digested by the lysozyme. The resulting nutrients diffuse into the cytoplasm and are assimilated

·         Undigested material is left behind when the Amoeba sp. moves away

3. What is the difference between a tissue and an organ?

A tissue is a group of specialised cells with a common structure and function, where as an organ is formed by two or more types of tissues working together to perform particular functions.

4. What are the major systems in humans?

The major systems in humans are;

·         Nervous system

·         Skeletal system

·         Circulatory system

·         Digestive system

·         Respiratory system

·         Excretory system

·         Reproductive systems

·         Muscular system

·         Integumentary system

·         Endocrine system

·         Lymphatic system

5. Name the systems that are involved in regulating the concentrations of oxygen and carbon dioxide in the bloodstream.

The systems that are involved in regulating the concentrations of oxygen and carbon dioxide in the bloodstream are cirulatory system and respiration system.

Focus Practice 2.3 (page 35)

1. List all the different types of tissues that make up the connective tissue. Briefly describe the function of each type of tissue named.

	Type of tissues	Function
1	Cartilage	·         Provides support to the nose, ears, and covers the ends of bones at joints. ·         Also forms dics between the vetebrate, this enables them to act as cushions to absorb pressure
2	Bone	·         Provide protection to organs in the body and supports the body
3	Blood cells	·         Has regulating, tranporting and protective functions. ·         Transports nutrients and oxygen to cells and removes carbon dioxide and waste products from the cells
4	Adipose tissues	·        Acts as an energy reserve ·        Provides insulation an protection

2. What are the different tissues that make up a leaf? Give the function of each type tissue in the leaf.

	Type of tissues	Function
1	Epidermal tissues	·         The cuticle on the epidermal on epidermal tisssue minimies water loss through evaporation ·         Protects the plant from mechanical injury ·         Prevents invasion of diseases caused by microorganisms
2	Ground tissues	·         Produces food by photosynthesis and stores food produced ·         Provides support and strengthens the plant
3	Vascular tissues	·         Tranports water and mineral salts from roots to the stems and leaves by the xylem tissues ·         Transports dissolved nutrients such as glucose from the leaves to the roots and stems by phloem tissues ·         Xylem also provide support to the plants

3. Discuss the process taking place in Figure 2.12. Predict the outcome if the cell does not have the Golgi apparatus.

          Process : Protein synthesis

-                   Synthesis of proteins takes place in the ribosomes.Ribosomes use information carried by the chromosomes to make these proteins.

-                   The rough ER transports proteins made by the ribosomes.

-                   Proteins are enclosed in vesicles before the proteins are secreted from the rough ER.

-                   Trnsports vesicle carrying proteins from the ER fuse with the membrane of the Golgi apparatus and empty their contents into the membranous space.

-                   These proteins are modified as tehy pass through the Golgi apparatus.

-                   The Golgi apparatus will then sort these products and package them into vesicles.

-                   Vesicles containing these products bud off form the Golgi membrane and travel them to other parts of the cells or to the plasma membrane.

-                   These vesicles will then fuse with the plasma membrane before releasing their contents outside of the cells.

·                     Prediction :

-                   The apparatus functions as a processing, packaging and transporting centre of carbohydrates, proteins phospholipids and glycoproteins cannot occur.

Activity 2.5 (page 33)

1.                  Why do cells need to maintain an optimal internal environment ?

   

 So that cells can function efficiently.

2.                  State the factors that affect the internal environment of an organism. Explain using an example.

    

            2 factors that affect the internal environment – physical factors and chemical compositions

            Physical factors – example : temperature, blood pressure, osmotic pressure

            Chemical factor – example : salt, sugar content, pH

- The metabolism of the body is affected by the changes in the chemical factors such as glucose and oxygen levels and physical factors such as temperature and osmotic pressure.

3.                  Why is it important for an animal to maintain relatively constant conditions in its 

            internal environment ?

     

The ability of organisms to maintain a stable environment enables them to live in a wider range of habitat. For example, mammals have highly developed internal  mechanisms to keep the body temperature around 37˚C despite considerable   variations in the external temperature.

4.                  Do you think a similar regulatory system exists in plants ? Explain why.

            In plants, the need for a regulatory system is lesser because

·         most plant cells are dead at functional maturity, and therefore chemical reactions 

            do not take place in these cells.

·         plant cells are not bathed in fluid but surrounded by air.

·         plant cells do not lyse in a hypotonic environment because they have cell walls.

·         water movement in plants is aided by natural factors such as transpirational pull.   

Assessment (page 39)

SECTION B

1. Figure 1 shows a unicellular organism.

a)      Explain how the organism in Figure 1 moves.

  

Amoeba sp. Moves with the help of pseudopodium (false-foot). Pseudopodium is an extension of the cytoplasm. The rest of the cytoplasm slowly flows into this extension, hence moving the organism along. Pseudopodium can be extended out in any directions.

b)      Name the structure labeled X.  State the main function of  X

Nucleus – controls and regulates all the activity of the cell

- contains the heredity factors responsible for the traits of the animals and  plants  

c)      Describe how the organism feeds.

Amoeba sp. feeds by a process called phagocytosis. It simply move round the food particles and enclose the food which is then packaged in a food vacuole. The fod vacuole fuses with a lysosome and the food is digested by hydrolytic enzyme called lysozyme. The resulting nutrients are absorbed into the cytoplasm. (refer figure 2.3, page 23)

d)      (i)  How does the organism reproduce ?

Amoeba sp. reproduce by binary fission. Its nucleus divides to form daughter     nuclei. The cytoplasm then divide and 2 daughter amoeba are form.

           ( ii ) Draw diagrams to show the reproduction process of the organism and label    

                   them

                 

       Refer figure 2.4 page 23

e)      Explain why the structure of the unicellular organism is more complex than the cells in the human body.

Unicellular organisms carry out all vital functions within a single cell. It feed, respire, excrete, move, respond to stimuli, reproduce and grow within its cell. Their survival depends largely on its cellular components which include the organelles. It does not have organ or system so the structure of the unicellular organism is more complex than cells in human body.

2. Figure 2 shows four different types of organelles.

Use the letters P, Q, R and S to match the following functions to the organelles.

  (a)

Function	Organelle
The site where cellular respiration occurs and energy is generated.	P
The organelle that captures light energy to make food	S
The organelle that functions as the processing, packaging and transporting centre of carbohydrates, proteins, phospholipids and glycoproteins.	R
A\series of membranes in the cytoplasm through which substances can be transported	Q

(b)    What organelles are present in plant cells but not in animal cells ?

S

(c)     Why is organelle P present in large numbers in the sperm cells of humans and flight muscle cells of birds ?

Sperm cells of human and flight muscle of birds have large number of mitochondria because the sperm cells require energy to propel through the uterus towards the fallopian tubes so that fertilization can take place, the flight muscle cells of birds contract and relax to enable movement and flight.

SECTION C

1. Figure 3 shows two different types of cells, labeled A and B

(a)    Which is a plant cell?  Give one reason for your answer.

B is a plant cell.

Reason:

-cell B have cell wall but cell A do not/

-cell B have fixed shape but cell A do not/

-cell B have chloroplast but cell A do not/

-cell B have large central vacuole but cell A do not have or small vacuole

(b)    Describe briefly how to prepare a slide of plant cells.

i)              Obtain a scale leaf from an onion bulb as shown in figure 2.1 (a) (Refer pg 9).

ii)            Using a pair of forceps, peel off the transparent epidermis from the inner surface of the onion scale leaf.

iii)          Put a drop of water onto the middle of the slide and place the epidermis on the drop of water (figure 2.1 (b) ). (Refer pg 9)

iv)          With the help of a mounting needle, cover the specimen with a cover slip at a 45° angle (figure 2.1 (c) ) (Refer pf 9)

v)            Add a drop of iodine solution onto one side of the cover slip.  Place a filter paper at the opposite end of the cover slip to allow the iodine solution to spread through the epidermis (figure 2.1 (d) ) (Refer pg 9)

vi)          Use a piece of filter paper to absorb the excess iodine solution.

vii)        Examine the slide under a light microscope using the low power objective lens and then the high power objective lens.

viii)      Draw the epidermis and label the cell structures which can be observed.  Record the magnification used.

(c)    By giving appropriate examples, describes how different organelles work together to enable the cell to function in an orderly manner.

i)        Synthesis of proteins, such as enzymes, takes place in the ribosomes.  Ribosomes use information carried by the chromosomes to make these proteins.

ii)      The rough endoplasmic reticulum transports protein made by the ribosomes.  Proteins that depart from the rough endoplasmic reticulum are enclosed in vesicles.  These proteins can be transported from one part of the cell to another. 

iii)    These protein are modified as they pass through the Golgi apparatus.  The golgi apparatus will then sort these products and package them into vesicles. 

iv)    Vesicles containing these products bud off from the Golgi membrane and travel to other parts of the cell or to the plasma membrane.  These vesicles will then fuse with the plasma membrane before releasing their contents outside the cell.

2. Describe briefly how cells are organized in a multicellular organism. 

Figure 4 (a) shows cells found on the lining of the trachea and figure 4 (b)  shows a type of vascular tissue found in plants.

(a)    Cell organisation in multicellular organization be summarized as follows :

Cells ------> tissues ------> organs ------> system ------> multicellular organism

·         Cells -  basic unit of life

·         Tissues – similar cells performing a particular function

·         Organ – A group of organs

·         Organisms – Made up of all the systems that work together.  The function of all the systems must be coordinated to work together for the survival of the organisms.

   

(b)   Describe how the cells in Figure 4 (a)  and 4 (b)  differ from a typical animal and plant cells respectively.

The epithelial tissue that live the trachea consists of elongated cells with hair like projection called cilia.  They also screate mucus.  The mucus traps dust particles while the cilia sweep the impurities away from the lungs.

The phloem consist of sieve tube and companion cells.  The sieve tube have pores of both end, so that it can transport organic nutrients from the leaves to storage organs or growing parts of the plants.

 (c)

An organ is made up of many types of tissues.  The function of an organ is therefore related to the types of tissues that make up the organ.

Explain the validity of the above statement using suitable diagrams.

• Stomach is made up of different tissues. 

 

                Each type of tissue performs a particular function. 

               Outer layer of stomach is made up of epithelial tissue which forms a protective layer.

  Inner layer of stomach is made up of epithelial glands to secrete enzymes and mucus.

 Smooth muscle tissue found in abundance in the stomach helps in digestion of food.

 Contraction and relaxation of the muscle tissues churn and mix the food.

 Connective tissue in the stomach such as collagen fibres gives elasticity to the stomach.

 Connective tissues such as blood supply oxygen to the stomach.