the organisation of cells

cells, tissues and organ systems

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definition of tissues

multicellular organisms are made up of specialised cells:

  • specialised cells are grouped into cells known as tissues
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definition of tissue

  • tissues consist of one or more types of cells all carrying out a particular function in the body (tssues do not operate in isolation)
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organs definition

  • an organ is made up of a group of tissue that are grouped into a structure so they can work effectively together
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organs in the human body

  • brain
  • liver
  • lungs
  • heart
  • small and large intestine stomach
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system definition

  • a number of organs working together as a system to carry out large scale functions in the body
  • e.g the digestive system includes stomach, small and large intestines
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plant system

  • the leaf is the equivilant plant system it is an organ that is composed of vascular tissue, epithelial tissue and mesophyll tissue
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different types of specialised cell

  • Simple squamous: flat tissue commonly found in the surface of blood vessels, and walls of the capillaries and lining of the avioli because it is thin an easy to diffuse through
  • Cuboida: cube like lines many other tubes in the body
  • Columnar: also lines tubes
  • Ciciliated: epithelials often contain goblet cells which produce mucus, so they are found lining the tubes in the lungs and the oviducts where regular waving of the cilia moves substances along the tubes
  • Compound stratified: epithelials are found on the surface of the skin, as it is constantly being scratched and abrased so it needs layers of cells
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other tissues in the body

  • Muscle tissue
  • nervous tissue
  • collagen tissue
  • elastin tissuefound in the artery wall
  • glandular tissue that secrets substances from inside the cells
  • connective tissue main support for the body
  • and includes bone and cartalige tissue
  • packing tissue that supports and protects some organs
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cell division- asexual reproduction- definition

  • Asexual reproduction - the production of genetically identicle offspring from a single parent cell or organism - and growth are both the result of miotic cell division
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Mitosis - definition

  • the chromosomes of a cell are duplicated and the genetic infomationis then equally shared out between the two daughter cells that result
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what are chromosomes

  • A chromosome is made up of a mass of coiled threads of DNA and proteins
  • when the cell starts to activel divide the chromosomes condense- becoming shorter and denser.(they take up stains readily and can be easily identified in this stage).
  • DNA molecules condense they are packaged using positively charged proteins called histones, DNA winds around the Histones forming a dense cluster called a nucleosomes. theses allow super coiling
  • every cell contains a characteristic number of chromosomes - humans have 46, they occur in matching pairs, in mitosis the two cells recieve a full set of chromosomes, as they are divided equally between the two cells resulting in compleate and identical set of DNA  
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Cell cycle

  • cells divide on a regular basis to bring about growth and asexual reproduction.
  • they divide in a sequence of events called the cell cycle :
  •  there is a period of active cell division known as mitosis, when an increase in the number of cells take place.
  •  this is followed by a period of non division known as interface , when the cell increases in mass and size, treplicate the dna and carry out normal cellular functions.
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cell cycle stages:

  • Growth 1 = cell carries out normal function
  • Synthesis = DNA is synthesised chromosomes supercoil, become dense in prepariation fo seperation
  • Growth 2 = prepairation for division increase in cell size
  • Mitosis = genetic division inclusing (interphase, prophase, metaphase, anaphase and telophase)
  • Cytokanisis = physical cell division splitting of cell membrane
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control of the cell cycle

Brought about by a number of checkpoints where the cell oves from one phase to the next

control chemicals are small proteins called = cyclines

they build up and attach to enzymes called cyclin-dependant kinases (CDK)

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process of cell division where the chromosomes are duplicated, forming two identical daughter cells there are 4 stages:

  • Interphase - tangled mats of chromosomes fills the nucleus and becomes replicated
  • Prophase - chromosomes condense and become visible, centriols migrate to the poles and become visible and spindles begin to form
  • Metaphase - nuclear envelope dissapears, chromosomes line up down the equator of the cell and attach to spindles at the centromere
  • Anaphase - chromatids are seperated and pulled anlong the spindle to a pole
  • Telophase early - chromatids reach the poles become known as chromosomes membrane begins reforming and the cytoplasm starts to divide
  • Telophase late - chromosomes decondense, nuclear membrane and nuclioli are fully reformed and centrols are present again , continues until two new identical cells are formed - cytokinesis- in animal cell the cell membrane pulls apart, in plants a cellulose cell wall builds and divivdes them
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stages of mitosis animal cell

interphase prophase metaphase anaphase telophase(

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mitosis in plant cell (cytokinisis)

  • Late telophase-
  • some spindle fibres remain nad guide the golgi vesicles to the equator of the cell
  • the vesicles enlarge and fuse together, forming a cell plate
  • the basic structure of a cell wall forms within each vesicle, and the vesicles fuse to join the cell wall together. small gaps left between the vesicles form plasmodesmata.
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stages of mitosis in plant cell vs animal cell

  • (
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observation of mitosis-stained section of root tip

Investigation into mitosis- need:

  • microscope-observation
  • waterbath 60 degrees
  • hydrochloric acid- to corrode cell walls making it easier to see under microscope
  • Scissors
  • dish or watch glass
  • beaker
  • scalpel
  • microscope slide
  • coverslip
  • stain- either Ethano-orcein stain, Toluidine blue

health & safty - Take care with ethanoic alcohol, hot hydrochloric acid and with the stain. Wear eye protection when handling these.(goggles)
Carry scalpels with care – hold them on a tile as you walk around the laboratory.

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investigation method

a Cut off 1-2 cm of the root tips. Put in a small volume of ethanoic acid on a watchglass (or other shallow dish) for 10 minutes.
b Meanwhile, heat 10-25 cm3 of 1 M hydrochloric acid to 60 °C in a water bath.

c Wash the root tips in cold water for 4-5 minutes and dry on filter paper.

d Use a mounted needle to transfer the root tips to the hot hydrochloric acid (see b) and leave for 5 minutes.

e Wash the root tips again in cold water for 4-5 minutes and dry on filter paper.

f Use the mounted needle to remove two root tips onto a clean microscope slide.

g Cut each about 2 mm from the growing root tip. Discard the rest, but keep the tips. note 2)

h Add a small drop of stain and leave for 2 minutes (note 3 and note 5).

i Break up the tissue with a mounted needle.

j Cover with a coverslip and squash

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