4.6 The leaf as an organ
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4.7 Summary (ESG78)
Section 7: Chapter Summary
- A tissue is a group of cells grouped together and working together.
- An organ is group of tissues grouped together and working together.
- Plant tissues include xylem, phloem, collenchyma, sclerenchyma, epidermis and meristematic tissue.
- Animal tissues include epithelial tissue, connective tissue, muscle tissue and nerve tissue.
- Plant and animal tissues are used in traditional technology, medical technology and cloning processes.
- The leaf is an example of a plant organ and its structure is adapted to its role in photosynthesis.
- Cells which are similar in structure group together to form tissues performing a particular function. Tissues form organs which combine to allow organisms to exist.
- Plant and animal cells have structures related to their functions.
- Plant tissues are broadly divided into Dividing or Meristematic and Permanent tissues.
- Meristematic cells are small, have high amounts of cytoplasm and a large nucleus to assist in their role in cell division.
- Permanent tissues are further divided into simple permanent (which have only one type of cell) and complex permanent (which have different types of cell coming together to perform a particular function). The simple permanent tissues include (with their function in brackets): Epidermis (protection), Parenchyma (storage), Collenchyma (support) and Sclerenchyma tissues (strength and structural support). Complex tissues are made up of the xylem and phloem.
- Xylem tissue is important in the transport of water and mineral salts. Phloem tissue is structured to allow the transport of organic compounds required for the plant (typically in the form of sucrose). Together the parenchyma, collenchyma and sclerenchyma are referred to as ground tissue. The xylem and phloem make up the vascular tissue.
- Animal tissues are made up of epithelial, connective, muscle and nerve tissue.
- Epithelium is made up of flat squamous cells, cuboidal cells or columnar cells in single or multiple layers. Epithelial cells are involves in secretion of enzymes, protective substances such as mucus and they provide a supportive function.
- Muscle tissue is made up of cardiac muscle, skeletal muscle and smooth muscle. Cardiac and skeletal muscle are striated. Smooth muscle and cardiac muscle are involuntary muscles whereas skeletal muscle is under voluntary control.
- Connective tissues are composed of areolar and fibrous connective tissues, cartilage, bone and blood. They provide strength and support, reduce friction and act as shock absorbers.
- Blood is made up of red blood cells (transport oxygen), white blood cells (responsible for immune response) and platelets (important in blood clotting).
- Nerve tissue is responsible for receiving stimuli from the environment (sensory neurons), processing it (interneurons) and sending impulses to muscles or glands (motor neurons) so that we can respond to the stimuli.
- Traditional healers and traditional medicine is an application of indigenous knowledge of plant and animal tissues.
- Modern Biotechnology is focused on a variety of applications of technology.
- Vaccines and antibiotics enhance the body's immunity. Vaccines rely on T-memory-cell derived immunity to fight subsequent infections.
- Immunity relies on the natural mechanisms (skin, mucus etc) as well as cellular mechanisms (T-cells and B-cells) fighting viral and bacterial infections.
- Blood transfusion is a way of replacing lost blood. It requires accurate blood type matching.
- Cloning of plant tissues requires either a piece of the plant tissue through vegetative propagation or chemical treatment to produce calluses in tissue culture propagation.
- Cloning of animal tissues occurs through the process of reproductive cloning. It can result in the replacement of a whole organism or, through therapeutic cloning the creation of stem cells.
- There are broad legal and ethical questions regarding cloning of organisms as well as the use of stem cells. These differ from country to country.
The leaf as an organ
- Plant leaf is an example of an organ, as it consists of a group of tissues that form part of a structural unit performing a common function.
- Plant leaves are adapted to absorb light in order for photosynthesis to occur as well as to manufacture sugars for transport to the rest of the plant.
- The major processes for which leaves are therefore adapted are photosynthesis, transpiration and gaseous exchange. Leaves transport oxygen, carbon dioxide, water and sucrose.
- Water is lost from the plant through transpiration out of stomata in the leaf. The movement of carbon dioxide and oxygen is through diffusion in and out of the leaf stomata.
- Sugar manufactured in the leaf is transported through the phloem vessel.
- Stomata open and close in response to a variety of environmental stimuli.
4.6 The leaf as an organ
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