Biology Chapter 2

• Mitochondria

  It is rod-shaped or spherical

  • It consists of two layers of membranes, which are the smooth outer membrane and folded inner membrane

  • Contains enzymes that play a role in cellular respiration

  Function:

  • A site that generates energy through the glucose oxidation process during cellular respiration

  • Energy released in the form of ATP molecules (adenosine triphosphate) to be used by the cells
• CENTRIOLE

  • Small cylindrical components that exist in pairs in animal cells
  • • Made up of complex arrangement of microtubules
  • • Does not exist in plant cells
  • Functions - Forms spindle fibre during cell division in animal cells
• GOLGI APPARATUS

  • Consists of a stack of parallel flattened sacs that are coated by a single cell membrane • New membrane is added at one end of the Golgi apparatus and vesicles bud off from the other end.
  • Function: Processes, modifies, packs and transports chemicals such as protein, carbohydrate and glycoprotein (combination of carbohydrate and protein)
• PLASMA MEMBRANE

  Outer membrane that surrounds the entire content of cell

  • Made of proteins and phospholipids

  • Thin and elastic film

  • Partially permeable

  Function:

  • Separates content of cell from the external environment

  • Controls movement of substances into and out of the cell

  • Allows exchange of nutrients, respiratory gases and waste materials between cells and their surroundings
• LYSOSOME

  Small spherical sac enclosed in a single membrane

  • Contains hydrolytic enzymes

  Function:

  • Hydrolyses complex organic molecules such as protein, nucleic acid and lipid

  • Breaks down bacteria and components of damaged cells
• NUCLEUS (PLURAL: NUCLEI)

  Largest component in the cell

  • Spherical, compressed and enclosed in a nuclear membrane with many pores

  • The nucleus contains chromosomes, nucleolus and nucleoplasm.

  Function:

  • Controls all cell activities

  • Has chromosomes that contain deoxyribonucleic acid (DNA). DNA determines the cell characteristics and metabolic function.
• RIBOSOME

  Small, compact and spherical granules

  • Consists of protein and ribonucleic acid (RNA)

  • Ribosomes are present on the surface of the rough endoplasmic reticulum or exist freely in the cytoplasm.

  Function: • Site for protein synthesis
• VACUOLE

  Liquid-filled sac, which is the cell sap.

  • A vacuole is surrounded by the tonoplast membrane.

  • Young plant cells have many small vacuoles while mature plant cells have a large vacuole.

  • The vacuole in animal cells is small.

  • Cell sap contains water, organic acids, sugars, amino acids, enzymes, mineral salts, oxygen, carbon dioxide and metabolic by-products.

  Function:

  • Water is absorbed into the vacuole plant cell and the cell becomes turgid.

  • In unicellular animals, the vacuole contracts during osmoregulation, osmosis and excretion.
• CHLOROPLAST

  Oval shaped

  • Consists of two layers of membrane

  • Contains chlorophyll pigments in the grana that give plants a green colour

  Function:

  Chlorophyll absorbs sunlight and converts it to chemical energy during photosynthesis.
• CYTOPLASM

  Consists of a jelly-like medium that contains components of the suspended cells

  • Contains organic compounds (such as protein, lipid and carbohydrate) and inorganic compounds (such as potassium ions)

  Function: Acts as a medium for biochemical reactions in cells
• CELL WALL

  A strong and rigid outer layer

  • Made from cellulose fibre

  • Fully permeable

  Function:

  • Maintains the shape of plant cells

  • Provides mechanical support to plant cells
• Similiarities Of Plant Cells and Animal Cells

  Both cells are made of nucleus, cytoplasm, plasma membrane, Golgi apparatus, mitochondrion, endoplasmic reticulum and ribosomes.
• Differences in Plant Cell and Animal Cell

  • Plant Cell - Has a fixed shape • Has a cell wall • Has chloroplasts • Has a large vacuole • Stores carbohydrate in the form of starch • Does not have a centriole
  • Animal Cell - Does not have a fixed shape • Does not have a cell wall • Does not have chloroplasts • No vacuole/if present, it is small • Stores carbohydrate in the form of glycogen • Has centrioles
• State one structural difference between the rough endoplasmic reticulum and the smooth endoplasmic reticulum.

  Rough endoplasmic reticulum has ribosomes

  attached it whereas smooth endoplasmic reticulum

  does not have any ribosomes attached to it.
• Why is the use of an electron microscope important in studying cells?

  Light microscope usually has a magnification

  of 1000x. On the other hand, the electron

  microscope is able to magnify a cell as much as

  2000000x. Without an electron microscope, cell

  structures cannot be seen clearly because the

  light microscopes can only observe certain cell

  components, such as cell membrane, cell wall,

  nucleus, cytoplasm, and chloroplast only.
• Chloroplast is found in some plant cells only. Give one example of a plant cell that does not have chloroplast and give your reasons.

  Onion cell because onions grow in the ground.

  Onions obtain food from their storage organs which

  are onion bulbs.
• Compare and contrast animal cells and plant cells.

  Similarities:

  Both cells have nucleus, cytoplasm, plasma

  membrane, Golgi apparatus, mitochondria,

  endoplasmic reticulums and ribosomes.

  Differences:

  • Plant cells have a fixed cell shape whereas

  animal cells do not have.

  • Plant cells have cell walls whereas animal cells

  do not.

  • Plant cells have chloroplasts whereas animal

  cells do not.

  • Plant cells have large vacuoles, whereas animal

  cells do not (if there is, the size is small).

  • Plant cells do not have centrioles whereas animal

  cells do.
• Unicellular organisms carry out all life processes:

  respiration, movement, nutrition, responding to stimulus, reproduction, growth and excretion.
• Unicellular Organism Movement

  Amoeba sp. constantly changes its shape when it encounters obstacles. Amoeba sp. moves by extending out its pseudopodium (false feet). This is followed by the flow of cytoplasm into the extended pseudopodium.

  • Paramecium sp. moves using rhythmic cilia beats.
• Unicellular Organisms RESPONDING TO STIMULI

  • Amoeba sp. and Paramecium sp. respond to stimuli such as chemicals, touch or bright light by moving away from the stimuli.
• Unicellular Organisms NUTRITION

  1. Amoeba sp. moves towards food by extending its pseudopodium to trap food particles by phagocytosis (Figure 2.3). For Paramecium sp. the presence of cilium beat helps transfer food particles into the oral groove.
  2. The food vacuole is combined with lysosome. The food particles are hydrolysed by the enzyme lysozyme in the lysosomes.
  3. The nutrients are absorbed into the cytoplasm.
  4. Undigested food is discharged when the Amoeba sp. moves. Undigested food in the Paramecium sp. is discharged through the anus.
• Unicellular Organisms RESPIRATION

  Exchange of oxygen and carbon dioxide gases occur through the plasma membrane by simple diffusion on the surface of the cell.
• Unicellular Organisms GROWTH

  Ameoba sp. and Paramecium sp. grow by synthesising new cytoplasm.
• Unicellular Organisms EXCRETION

  • Waste such as carbon dioxide and ammonia are removed by diffusion.

  • As Amoeba sp. and Paramecium sp. live in freshwater environments, water will diffuse by osmosis and fill the contractile vacuole.

  • When the vacuole expands to the maximum size, contraction occurs and water is excreted from time to time.

  • This process is called osmoregulation.
• Unicellular Organisms REPRODUCTION

  When the conditions are suitable and there is plenty of food, Amoeba sp. and Paramecium sp. will reproduce via asexual reproduction that is binary fission through mitosis. • However, when the environmental conditions are not suitable, such as dry conditions, low temperature and food shortage, the Amoeba sp. forms spores that will only germinate when the environment improves. • For Paramecium sp., sexual reproduction, that is conjugation occurs when environmental conditions are not suitable.
• What is the function of the contractile vacuole in a Paramecium sp.?

  Contractile vacuoles are involved in osmoregulation.
• How does the Amoeba sp. move?

  Amoeba sp. moves by extending its pseudopodium

  (false feet). This is followed by cytoplasmic

  streaming into the extended pseudopodium.
• How does the Amoeba sp. reproduce when the environment is unfavourable?

  Amoeba sp. forms spores. In the spores, mitosis

  takes place multiple times to form daughter cells.

  Once environmental conditions improve, the spores

  will germinate and release daughter cells.
• Predict what will happen to the contractile vacuole if the Paramecium sp. is placed in a concentrated salt solution.

  The contracting rate of the contractile vacuole will

  decrease.
• Multicellular Organisms MUSCLE CELL

  • Arranged as multinuclear striated fibres • Contract and relax to generate movement
• Multicellular Organisms NERVE CELL

  Long and thin in shape • Functions in sending nerve impulses
• Multicellular Organisms WHITE BLOOD CELL

  Can change shape • Functions in destroying pathogens
• Multicellular Organisms EPITHELIAL CELL

  Thin and flat cells • Coats the surface of organs such as the digestive tract
• Multicellular Organisms RED BLOOD CELL

  • Does not contain a nucleus • Shaped as a biconcave disc • Functions to optimise transportation of oxygen
• Multicellular Organisms SPERM CELL

  • Has a long tail to enable it to swim towards the ovum in the Fallopian tube • The head carries a set of chromosomes from the male
• Multicellular Organisms SIEVE TUBE ELEMENT

  • Long cylindrical tubes arranged from end to end • Transports organic materials from leaves to storage organs such as fruits
• Multicellular Organism XYLEM VESSEL

  Long, continuous hollow tube • Functions in transporting water and mineral salts from the roots to the other parts of the plant
• Multicellular Organism PALISADE MESOPHYLL CELL

  Consists of long cylindrical cells, arranged vertically and close to each other • Contains high chlorophyll density • This arrangement allows maximum absorption of sunlight for photosynthesis
• Multicellular Organism SPONGY MESOPHYLL CELL

  Cells are loosely arranged with lots of air space in between • Large air space allows exchange of gas from the inside of the leaves to the palisade mesophyll cells
• Multicellular Organism GUARD CELL

  Modified lower epidermal cells with the thicker cell wall on the inner side • Controls the opening and closing of the stoma. Stoma is the opening that allows the exchange of oxygen and carbon dioxide