Cells

• Cells

  The basic units of life that carry out the life process

  e.g. muscle cell, root cell
• Unicellular

  Organisms that consist of only one cell

  e.g. Amoeba, Protozoa
• Multicellular

  Organisms that consist of more than one cell

  e.g. Animals, Plants
• Red Blood Cells

  • No nucleus
  • More room for the haemoglobin
  • Biconcave shape
  • Quite small (7μm)
  • 120 days cycle
  • Squeeze through narrow blood vessels to deliver oxygen to every other cells
• Fat Cells

  • The nucleus and cytoplasm are squeezed to the side to make room
  • Act as an energy store for times when you can't eat enough
  • A layer of them under your chin also helps to keep you warm
• Nerve Cells

  • A nerve cell(neuron) consists of a large cell body and nerve fibres
  • One elongated extension(axon) for sending impulses and usually many branches(dendrites) for receiving impulses
  • The impulses from the axon cross a synapse (the junction between two nerve cells) to the dendrite of another cell
• Muscle Cells

  • Muscle cells are long and thin
  • Designed to work together
  • Pull on bones are grouped into bundles while the muscle cells in the heart are linked together
  • Completely full of fibres, so its nucleus is squeezed to the side
  • The fibres allow muscles cells to contract and produce movement
• Organelles

  A cell has many organelles. Organelles are groups of complex substances inside a cell which carry out specific functions within the cell.
• Protoplasm

  Living contents of a cell that is surrounded by a cell membrane.
• Nucelus

  • Contains hereditary materials called chromosomes which are made up of DNA. The information that DNA contains is passed from one generation to the next.
  • The 'control centre' as it controls all the activities in a cell such as growth and repair
• Cell membrane

  • Forms a boundary between cytoplasm and the outside of the cell
  • A semi-(or partially or selectively) permeable membrane which allows certain substances to pass through only
  • Controls the movement of substances in and out of the cell
• Cytoplasm

  • Gel-like fluid in which many organelles and dissolved chemicals are found
  • Made up of water mainly
  • Where most chemical reactions take place
• Vacuole

  • Membrane bound bubbles
  • Animal cells have small and numerous vacuoles
  • Plant cells have one large central vacuole
  • In animal cells, vacuoles store dissolved nutrients and mineral salts
  • In plant cells, it is filled with cell sap which stores nutrients and mineral salts. It also provides turgidity to the cell by pushing the cytoplasm outward against the cell wall
• Cell wall

  • Fully permeable
  • Contain cellulose
  • Give plant cells a regular shape
  • Protects plant cells from injury
• Chloroplasts

  • Surrounded by double membrane
  • Contain chlorophyll to absorb light energy for photosynthesis
• What is meant by a specialised cell?

  A cell that designed to do a particular/special task in an organism
• Plant cells' modifications

  Root hair cell

  • Has an elongated structure to increase the surface area so that absorption of water and mineral salts can take place quickly

  Palisade cell

  • Contains numerous chloroplasts to carry out photosynthesis more efficiently

  Xylem

  • Made up of thick and lignified wall to prevent the collapse of the vessel
  • Hollow lumen to allow passage of water and mineral salts easily without obstruction
• What is meant by division of labour

  In multicellular organisms, division of labour refers to each type of cell that specialised in performing one particular function
• Two benefits of division of labour in multicellular organisms

  • Different function of multicellular organisms can be performed at the same time
  • It ensures smooth and efficient functioning of the organisms as a whole
• Why unicellular organisms do not need division of labour?

  Make up of only one cell, so they can obtain nutrients and remove waste products by simple diffusion
• The levels of cellular organisation

  cells > tissues > organs > organ system > organism
• Tissue

  • A group of similar or different cells working together to perform a similar function

  e.g.

  In animals

  • Connective tissue such as blood
  • Epithelial tissue such as epithelium
  • Muscle tissue such as muscle cells
  • Nerve tissue such as nerve cells

  In plants

  • Ground tissue such as cortex, palisade
  • Dermal tissue such as root hair, epidermis
  • Vascular tissue such as xylem, phloem
• Organs

  • A group of tissues working together for a particular function

  e.g.

  In animals

  • Heart, Lungs, Kidney

  In plants

  • Leaf, Stem, Roots
• Organ systems

  • A group of organs working together to perform a particular function

  e.g.

  In animals

  • The digestive system
  • The circulatory system
  • The respiratory system

  In plants

  • The shoot system
  • The root system
• Organisms

  • A group of organ systems working together to support a whole living organism

  e.g.

  In animals

  • Human

  In plants

  • Flowering plants
• Cell specialisation

  1. Not every cell in a multicellular organism performs the same task. In multicellular organisms, cells are modified to carry out specialised functions.
  2. A specialised cell is designed to do a particular task in an organism.
• Microscope

  1. A microscope magnifies an object by making it appear bigger than it actually is.
  2. It is a useful tool to observe very tiny objects which are not visible to the naked eye.
  3. When using a microscope, a glass slide containing the specimen is placed on the stage of the microscope.
• Eyepiece

  • To allow the users to look through the specimen
• Body tube

  • To maintain the proper distance between the eyepiece and the objectives
• Coarse focus knob

  • To allow initial focus of the specimen
• Nosepiece

  • To hold the objectives in place so that they can rotate and can be changed easily
• Objectives

  • To magnify the specimen in different sizes
• Stage

  • To hold the glass slide with its clip
  • To allow light to pass through the specimen through its opening
• Fine focus knob

  • To make small final focus adjustment to sharpen the focus
• Mirror or lamp

  • To provide a source of light to illuminate the specimen
• Specialised plant cells

  • Leaf cells absorb sunlight and make nutrients, while root cells are specialised to take in water and minerals.
  • The cells on the outside of this root are hair cells.
  • They have long, thin side branches.
  • These increase the surface area of the roots and make it easier for them to collect water and minerals from the soil around them.
  • Xylem cells from tough hollow tubes that carry water from the roots to rest of the plant.
  • Phloem cells are specialised to carry nutrients down from the leaves.
• Characteristics of living things

  1. Movement
  2. Respiration
  3. Sensitivity
  4. Growth
  5. Reproduction
  6. Excretion
  7. Nutrition
• Unlike plant cells, animal cells do not have a fixed shape because they do not have the rigid cellulose cell wall to keep them in a specific shape
• Red Blood Cells

  Contain haemoglobin that helps the transport of oxygen more efficiently

  • No nucleus in order to contain more haemoglobin
  • Biconcave shape to increase surface area for faster diffusion of oxygen
• Muscle cell

  Has fibres which involve in muscle contraction