Biology

• Cell surface membrane

  • Partially permeable
  • Allows only small molecules like water and glucose to pass through it but not the large ones like protein molecules
• function of cell surface membrane :

  Surrounds and holds the part of a cell together

  Control the passage of molecules in and out of cell
• cytoplasm

  It is a jelly like substance. It consists of water and dissolved substances such as salts,sugars and protein

  Function:

  It is the site of metabolic reaction

  Cytoplasm also contained specialised structures called organelles(mitochondria and ribosomes)
• Nucleus

  It consists chromatin. Chromatin is made up of coils of DNA bound to protein.

  During cell division: the chromatin condense to form chromosomes(long thread like structures).

  Every human has 23 pairs of chromosomes.

  Genes: contains genetic information for the all a particular protein.

  Nucleus : responsible for an organelle called ribosomes which manufacture protein.
• Mitochondria: are the sites of aerobic respiration during which food (glucose)is broken down to release energy. Ribosomes: are the sites of protein synthesis i.e. is the place where amino acids are joined together to make polypeptide.
• cell wall It is made up of a carbohydrate cold cellulose.

  It is fully permeable to water, gases, salts and sugars.

  Functions:

  It gives shapes, support and protection to the cell.

  When a plant cell is full with water, it is said to be turgid, this turgidity provides support to soft tissues of plant.
• Chloroplast

  • chloroplast contains a green pigment called chlorophyll.
  • This pigment traps light energy and converts it to chemical energy which is used to make food(glucose).
  • In chloroplast photosynthesis, occurs during which glucose is formed. Glucose is then converted to starch which stained blue black.
• Large central vacuole

  • It is a large space that contain a fluid called cell sap.
  • Cell sap contains water, salts, sugars, amino acid and other substances.
  • The large central vacuole is enclosed by a partially permeable membrane called tonoplast.
• Differences between animal cell and plant cell

  1. Cell wall is absent in animal cell but presents in plant cell.
  2. chloroplast is absent in animal cell but present in plant cell.
  3. Large central vacuole is absent in animal cell but present in plant cell.
  4. animal cell is circular whereas plant is rectangular.
  5. Animal cell is relatively smaller in size but plant cell is relatively larger in size.
  6. Storage carbohydrate is glycogen in animal whereas in plant cell storage carbohydrate is starch.
• Structure of bacteria cell

  • Bacteria are the smallest living organism and can only be seen with a microscope.
  • Bacteria cell does not contain and mitochondria and nucleus as it has circular DNA lies free in the cytoplasm.
  • Some bacteria have small rings of DNA called plasmids.
  • Some bacteria have flagellum which enable them to swim in a aqueous environment.
• Specialized cells

  Specialized cells are cells that have undergone changes in and sizes to perform specific functions. During a process called Differentation.
• Root hair cells

  Function:

  It absords water dissolved mineral salts from soil.

  Adaptations:

  It has a long and narrow root hair cell to increase its surface area for efficient absorption of water and mineral.

  The sap vacuole contains a concentration solution of salts and sugars to allow osmotic absorption of water
• Xylem vessel ( dead vessel )

  Xylem vessel consist of hollow dead cells arranged end to end to a long and narrow continuous tube. They have no protoplasm. They have only a cell wall and a strong material called lignin.
• Function of xylem vessel:

  They transport water and dissolved miners salts from the roots to stem, leaves, fruits and flowers.

  They provide mechanical support to the plant.

  Adaptation:

  It has a long and continuous hollow tube, with no cross walls, to allow easy flow of water amd mineral salts.

  The presence of lignin in its we all increases its mechanical strength to support the plant.

  Lignin also prevents the vessels fromm collapsing.
• Red blood cell (RBC)

  Function: Transport oxygen from the lungs to all part of the body.

  Adaptation:

  It contains the red pigment called hemoglobin which can combine with oxygen to form oxyhaemoglobin.

  Absence of nucleus provides more spaces for more hemoglobin and therefore more oxygen can be carried.

  They are bicincave to increase their surface area for efficient absorption of oxygen.
• Levels of organization in living organism


  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organism
• Cells


  Basic unit of life
• Tissue


  A group of cells having the same structure and work together to perform a specific function
• Tissues in animals


  • Muscle
  • Nerve
• Tissues in plants


  • Epidermis
  • Palisade
• Organ


  Consists of several tissues working together to perform a particular function
• Organs in animals


  • Heart
  • Lungs
  • Liver
• Organs in plants


  • Leaf
  • Stem
  • Root
  • Shoots
• Organ system


  Consists of several organs that work together to perform a particular set of functions
• Organ systems in animals


  • Digestive
  • Respiratory
• Organ systems in plants


  • Respiratory
  • Transport
• Organism


  A group of organ systems working together to keep it alive
• Organisms


  • Animals
  • Plants
  • Fungi
• Classification

  Classification is the process of classifying living organisms into difference groups depending in their characteristics and structure,shared with other organism.
• Classification systems groups:

  1. Species-group of organism that can reproduce their fertile offspring.
  2. Genus-group of similar and closely related species.
  3. Family-group of related genera
  4. Order-group of related families
  5. Class-group of similar orders
  6. Phylum-group of similar classes
  7. Kingdom-group of similar phyla
• The system of naming organisms is called binomial system because each organism is identified by scientific name consist of two words.

  Ex: homo sapien

  Genus species

  Felis tigris

  Genus species
• 5 kingdom namely: 

  1.Plants/plantae

  Main features

  1. They are multicellular.
  2. They contain chloroplast and can photosynthesise.
  3. They have cellulose cell wall, sap vacuole and nucleus
  4. They store carbohydrates as starch.
• 2. Animal/ animalia

  Main features

  1. They are multicellular
  2. They they have no chloroplast and no cell wall.
  3. They feeds on other organisms for foo
  4. They store carbohydrates : glycogen
  5. They have nuclues.