XII CHAPTER 1 HOMEOSTASIS
- Kiran Syed
- Jun 12, 2020
- 8 min read
Updated: Jun 29, 2020
HOMEOSTASIS
“HOMOIOS” means LIKE / SAME / RESEMBLING
“STASIS” means STATE (Condition)
Organisms, in order to live, have to maintain a steady internal environment to face the harsh fluctuating external conditions. Biologists term the maintenance of a steady state as homeostasis
Here, the term internal environment refers to “the environment of the cell” because living organisms are made up of cells.
Tissue fluid and sap are the environments of higher animals and plants, respectively.
The important aspects of internal environment that must be kept constant are:
Osmoregulation (regulation of osmotic pressure of cell determined by the relative concentration of solutes and water);
Excretion (removal of excess substances, unwanted or toxic metabolic by-products); and
Thermoregulation (regulation of temperature up to a tolerable limit).
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References:
cactus
https://www.freepik.com/premium-photo/heart-shaped-bunny-cactus-opuntia-mornig-sun_2216201.htm
Major fluid compartments.
http://what-when-how.com/nursing/fluid-and-electrolyte-balance-structure-and-function-nursing-part-1/
xylem and phloem http://webprojects.oit.ncsu.edu/project/bio181de/Lab/transport/transport2.html
Movement of fluid in xylem vs phloem http://webprojects.oit.ncsu.edu/project/bio181de/Lab/transport/transport2.html
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OSMOREGULATION (the regulation of solutes and water)
Water Relations of Cell:
Water is used as biological solvent, which drives most of the metabolic activities of a living cell. It moves in and out of the cell by a process called osmosis.
*metabolism is defined as the chemical processes that occur within a living organism in order to maintain life.
w
Osmosis
Water moves in and out of the cell by a process called osmosis, It is a special kind of diffusion in which water molecules move from higher concentration towards lower concentration across the plasma membrane.
Balance of water and solutes in the body:
Water Potential:
tendency of water to move from one area to another
The potential energy of water in the region of its higher concentration is greater than its potential energy in the region of lower concentration.
Water Potential is simply the capacity of a living system to lose water.
The concentration of a solution is biologically expressed either as water potential (in case of plants) or osmotic pressure (in case of animals) which shows relative (Comparative) amounts of water and solutes in the cell.
In case of plant cells, the water potential of cell sap (solution in vacuole) is termed as solute potential.
If a plant cell is placed in pure water or solution of higher water potential than the solution in its vacuole, the water moves from outside to inside the cell (endosmosis) and ultimately into the vacuole. As a result, the cell swells or becomes turgid. Such an external solution is called hypotonic.
Further allowing the cell into such hypotonic medium does not cause it to burst because the cell wall develops a tension causing an internal hydrostatic pressure or pressure potential due to which further uptake of water in cytoplasm is resisted and finally stops.
*pressure potential is the pressure exerted by the rigid cell wall that limits further water uptake.
On the contrary, if some animal cell is continuously placed in hypotonic solution, it bursts because the plasma membrane cannot resist the pressure potential. Thus within the bodies of higher animals, the tissue fluid is maintained at the same water potential, called isotonic, as the cell solution.
When a plant cell is placed in concentrated solution or hypertonic solution, there is a net movement of water out of the cell. As a result, the cell becomes flaccid, Under such condition, the cytoplasm with its plasma membrane shrinks from the cell wall. This condition is called plasmolysis.
*Plasmolysisis when plant cells lose water after being placed in a solution that has a higher concentration of solutes than the cell does.
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References:
Osmosis:
Water Potential:
Difference Between Isotonic Hypotonic and Hypertonic
Types of Solution
Effect of Osmosis on Plant Cell
Water Potential
Pressure Potential:
RBC video
Onion Cells Video:
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1.2.3 Osmoregulation in Plants:
Depending upon the availability of water to flowering plants in their natural habitat, they are grouped into four categories:
i) Hydrophytes,
ii) Halophytes,
iii) Mesophytes and
iv) Xerophytes.
i) Hydrophytes:
*hydro means water
*phyte means plant or plant like
The hydrophytes are those plants which grow in water or wet places. According to water relation, they are classified into three types.
1. Totally submerged plants:
They may be rooted or not. They remain within water e.g. Hydrilla, Vallisnaria.
2. Partialy submerged.
Leaves float on the surface, while other parts remain within water e.g. Nymphea (Water Lily)
3. Amphibious plants.
Roots and some part of stem with leaves within water willing water some above the water. They are also called marsh plants because they grow in shallow water. e.g Typha.
Adaptations of Hydrophytes:
*Adaptation: any change in the structure or behavior of a species which helps it to become better fitted to survive and reproduce in its environment.
They do not have any difficulty in obtaining water. The stems and leaves of hydrophytes generally lack cuticle or it is very poorly developed.
*The plant cuticle is an extracellular hydrophobic layer that covers the aerial epidermis of all land plants, providing protection against desiccation and external environmental stresses.
In partly submerged hydrophytes, where the leaves are floating on the surface of the water, stomata are only present on the upper epidermis as the lower epidermis is facing and in contact with the water. However, there are many stomata on the top of the leaf, and they are always open.
ii) Halophytes:
*halo means realted to saline (salt)
The plants growing in salt marshes close to sea are termed as halophytes. Some of the examples of halophytes are glasswort, cord-grass, etc.
They have to absorb water from such a soil, which has higher salt concentration and therefore lower water potential (higher osmotic pressure). Halophytes cope with this situation, by actively absorbing salts into their roots. As a consequence, the cells of the roots develop lower water potential which brings in water by osmosis.
The excess salt can be stored in cells or excreted out from salt glands on the leaves. The salt thus secreted by some species help them to trap water vapours from the air, which is being absorbed in liquid form by leaf cells. Therefore, this is another way for obtaining additional water from the air.
iii) Mesophytes:
*meso means middle/ intermediate.
These are most of the land plants of temperate zones, which grow in well watered soil. They can easily compensate the water lost by transpiration through absorbing water from the soil, To prevent excessive transpiration, they have developed a water proof external covering called cuticle.
They are intermediate between hydrophytes and xerophytes. They grow in moderatye temperature and adequate proportion of minerals and moisture content.
iv) Xerophytes:
*xero means dry
Plants living in dry places such as deserts, steep hills, etc have to face scarcity of water. They are termed as xerophytes. Under such conditions, water potential of soil and air are very low.
The xerophytes' have developed following adaptations to conserve water and to survive during drought conditions.
I-Seed/ Spores as adaptations in life cycle during drought condition:
Land plants produce seeds or" spores during their life cycle. The protoplasms of these structures are quite concentrated and usually protected externally by hard coats and thus these structures remain viable for a considerable period of time.
II - Adaptation for balance between transpiration and water uptake:
a) Development of very deep vertical roots for the better absorption of water from the soil as seen in Acacia, Banyan, etc.
b) Other plants such as Cacti have superficial, horizontal roots which can absorb water before it evaporates from the soil.
c) Reduction in number of stomata, Sunken type of stomata,
development of hairy epidermis, (creates a microclimate of still, humid air, reducing the water vapour potential gradient and minimising the loss of water by transpiration from the surface of the leaf.)
folding of leaves, reduction in size of lamina and modification into spines are some of the adaptations for reducing the rate of transpiration.
Some plants store water in large parenchymatous cells present in stem or leaves. Such plants are termed as succulents. As a result, the stem or leaves become juicy.
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References:
Hydrilla
http://plants.ifas.ufl.edu/plant-directory/hydrilla-verticillata/
Nymphea
https://sites.google.com/site/mdrklrd/terrestrial-flora/bladderwort
Nymphea under water
https://sites.google.com/site/mdrklrd/terrestrial-flora/bladderwort
Typha
https://simple.wikipedia.org/wiki/Typha
Typha
Adobe stock
Hydrophyte TS
https://visualsunlimited.photoshelter.com/galleries/I0000RfrRUigSSBI/435425-JPG
Thick cuticle
http://sta.uwi.edu/fst/lifesciences/bl11f/IMAGES/Epidermis%20D/02a%20Thick%20cuticle.html
Cross-section of Pondweed
https://www.naturepl.com/stock-photo-cross-section-of-pondweed-potamogeton-sp-hydrophytic-leaf-lm-x30-image01306505.html
glasswort
https://www.britannica.com/plant/glasswort
Osmosis
https://mammothmemory.net/biology/movement-in-and-out-of-cells/osmosis/examples-of-osmosis.html
SAlt Gland
https://www.sciencedirect.com/science/article/pii/S0254629909002816
Salt Crystals on leaf
https://asknature.org/strategy/glands-remove-excess-salt/attachment/salt-crystals-on-mangrove-leave/
Mesophyte example
https://en.ppt-online.org/220233
echeveria succulent
https://www.britannica.com/plant/xerophyte
Underground root illustration
https://mygrass.it/approfondimento-sui-tessuti-radici-e-foglie/
Cactus root network in desert environment, drawing
https://www.gettyimages.com/detail/news-photo/cactus-root-network-in-a-desert-environment-drawing-news-photo/929647084
Reduction in number of stomata, Sunken type of stomata,
https://www.sciencephoto.com/media/439109/view/mint-leaf-surface-sem
Sunken stomata
https://www.sciencephoto.com/media/30244/view/sem-of-spruce-needle-stomata
hairy epidermis
https://tentativeplantscientist.wordpress.com/
lamina and modification into spines
https://tentativeplantscientist.wordpress.com/
large parenchymatous cells
https://www.flickr.com/photos/joanna_25/31296566564
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EXCRETION
This aspect of homeostasis refers to the process of removal of metabolic wastes; excess substances such as salts, water, and toxic substances such as drugs from the body. However, in a restricted sense, it is the process of removal of nitrogenous metabolic wastes from the body of organism. Such wastes are formed as a consequence of proteins and nucleic acid metabolisms.
Excretion in Plants:
For a number of reasons, excretion in plants does not pose serious problems. First, the rate of catabolic processes is much less than the animals of same weight or mass. Thus metabolic wastes accumulate more slowly. Moreover, waste products of catabolism are used by green plants in their anabolic processes.
Green plants do not excrete nitrogenous wastes, on the contrary they recycle breakdown products of nitrogen metabolism. Secondly, the metabolism of plants is mostly carbohydrate based and its end products CO2 and water are far less harmful than the nitrogenous wastes produced by protein metabolism in animals.
As such plants do not possess any organ exclusively meant for excretion as in the case of animals. However, certain substances, which accumulate to levels in excess of plants needs, such as water, carbondioxide, oxygen and certain ions, are to be eliminated.
Transpiration
Plants get rid of surplus water by losing it in vapour form which diffuse out through stomata. This process is known as transpiration.
Guttation
Some land plants exude water from points called hydathodes found at the margins and tip of leaves. This loss of water in liquid form is known as guttation.
It is common in plants growing in tropical rain forests where rate of absorption is higher due to high rain fall and rate of transpiration is much low due to high humidity.
Green plants, in light, release oxygen because rate of photosynthesis is much higher than the rate of respiration. At dark, plants release CO2 because respiration is going on whereas photosynthesis is not. Ions present in excessive concentration combine with organic compounds and are deposited in dead cells such as heartwood and bark or in the cells which are at the point of their death.
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References:
Differences Between Catabolism and Anabolism
https://byjus.com/biology/differences-between-catabolism-and-anabolism/
respiration and photosynthesis reaction
https://www.quora.com/Is-it-true-that-plants-carry-out-photosynthesis-only-during-day-and-respiration-only-at-night-If-yes-Why
Transpiration
https://www.iconwater.com.au/Water-education/The-Natural-Water-Cycle/Transpiration.aspx
Guttation
https://www.botany.one/2017/07/hooray-for-the-hydathode/
Difference Between Guttation and Transpiration
https://pediaa.com/difference-between-guttation-and-transpiration/
Differences between Cellular Respiration and Photosynthesis
https://byjus.com/biology/difference-between-photosynthesis-and-respiration/
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THERMOREGULATION
It is the maintenance of body temperature within a range that enables the body to function efficiently. The normal temperature range for active life is 10°C to 35°C for most of the organisms. The temperature influences directly upon the membrane properties as well as metabolism of cells.
Adaptations of plants to low and high temperature:
Low temperature:
Low temperature affects the fluid nature of plasma membrane of plant cell. It is ultimately related to affect the transport of solutes across the membrane.
Under such conditions the plants cells increase the proportion of unsaturated fatty acids which prevent crystal formation.
The low temperature at the level of freezing point causes ice crystal formation in cell. This is avoided by the plants inhabiting cold regions by developing freezing tolerance in which the composition of solutes of cell is altered in a way that ice crystals are formed in the cell wall rather than the cytosol. The cytosol is super cooled below the freezing point without the formation of ice.
*cytosol is the liquid found inside cells.
*Supercooling is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid.
High temperature:
High temperature is more harmful than low temperature since enzymes are denatured, which is disastrous for metabolism. The principal way to cool down the plant in this situation is transpiration, i.e. evaporation of water mainly through stomata. At 40"C or above, most of the plant cells synthesize heat shock proteins that protect enzymes and other proteins from denaturing due to higher temperature. In addition to these mechanisms plants have some other ways of avoiding overheating such as shiny cuticle, a small leaf surface area, wilting, etc.
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References:
Difference Between Saturated and Unsaturated Fats
Extracellular Freezing
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