The Cell

The Cell

Cell Structure
1. Plant Cell
  1. Cell wall is made of cellulose
  2. The vacuole gives the cell strength and shape and may also store materials.
  3. Chloroplasts are green structures in which photosynthesis takes place.
2. General Cell Ultrastructure
  1. Cell membrane is composed of a phospholipid bilayer and proteins. Membranes retain cell contents. They control what eneters and leaves the cell. It gives some support.
  2. The nucleus is the control centre of the cell. It contains strands of DNA arranged into chromosomes. When chromosomes are not dividing they are called chromatin. Nuclear pores in the membrane allowed mRNA to pass in and out of the nucleus. The nucleoulus is stained dark. Ribosomes are made here.
  3. The cytoplasm is a jelly-like fluid within which all cell organelles are suspended.
  4. Mitochondria supply energy to the cell. They are sights of respiration.
  5. Ribosomes are made of RNA and protein. They make proteins by combining a sequence of amino acids to form a protein.
Cell Division
1. Cell continuity means all cells develop from pre-existing cells.
2. Chromosomes are coiled threads of DNA and protein that become visible in the nucleus at cell division.
3. A haploid cell has one set of chromosomes. A diploid cell has two sets of chromosomes.
4. A homologous pair consists of two chromosomes that each have genes for the same feature at the same positions.
5. Interphase is the phase in the cell cycle when the cell is not dividing. During interpahse, new organelles are produced.
6. Mitosis is a form of nuclear division in which one nucleus divides to form two identical nuclei. (PMAT)
  1. Prophase - chromatin contracts. Double stranded chromosomes are visible. The nucleolus disappears. Nuclear membrane breaks down.
  2. Metaphase - Spindle fibres attach to centromeres. Chromosomes line up across cell.
  3. Anaphase - Spindle fibres contract. Centromeres split. One strand is pulled to each pole.
  4. Telophase - Four chromosomes begin to lengthen. Spindle fibres break down. Nucleolus reforms. Nuclear membrane forms around each clump
7. Cell division in animals - A cleavage furrow appears around the cell. It becomes deeper and divides the cytoplasm until the cell divides in two.
8. Cell division in plants - Vesicles gather in the area between the two nuclei. They form a structure called the cell plate. Two cell walls form within the cell plate. The part in the middle is called the middle lamella.
Cell Diversity
1. A tissue is a group of similar cells that carry out the same function.
2. Plant Tissues
  1. Dermis tissue is the skin of the plant. it covers the leaves, stems and roots. Living rectangular cells with a thick cell wall. Its function is to protect the plant and prevent water loss (cuticle)
  2. Vascular tissue transports materials around the plant. It consists of two types of cells; xylem and phloem
3. Animal Tissues
  1. Connective tissue consists of a number of cells spread out in a matrix. e.g blood is a connective tissue containing white blood cells, red blood cells and platelets.
  2. Nervous tissue is composed of nerve cells called neurons. They are adapted to carry electrical impulses to and from the brain and spinal chord.
4. An organ is a number of different tissues that work together to carry out the same function. e.g the heart and a leaf.
5. An organ system is a number of organs working together to carry out one or more functions.
6. Tissue culture is the growth of cells in or on a sterile nutrient medium outside an organism
  1. Micropropagation is the growth of large numbers of plants from very small plant pieces. A large number of plants are produced in a short time. Plants are genetically identical and it is inexpensive
  2. Skin grafting is used to grow new skin for burn victims. Skin can be taken from a healthy part of the body and transplanted to the burned area. Stem cells are often used for this.

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