RHS Part 2
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what is the formula for photosynthesis
Describe internal structure of Monocot Stem and their functions
- Epidermis is outermost layer of the stem, made up of parenchymatous cells covered with cuticle.
- HypodermisThe monocot stem has a sclerenchymatous hypodermis lying below the epidermis and its gives mechanical strength to the plant
- Ground tissuesThere is no peculiarity into cortex, endodermis, pericycle, and pith and the entire mass of parenchymous cells lying inner to the hypodermis. It is
- made up of cellulose containing reserve food materials like starch. The cells of the ground tissue next to the hypodermis are small, varied in shape (polygonal), and compactly arranged. The function of the ground
- tissues to store food and for gaseous exchange.
- Vascular bundlesThey are scattered in ground tissues and each vascular bundle is surrounded
- by a sheath of sclerenchymatous fibres called bundle sheath. They are small, numerous, conjoint, collateral, endarch, and closely arranged in the peripheral portion.
- Phloem and xylem In monocot stem, the phloem consists of sieve tubes and companion cells
- and phloem parenchyma and phloem fibres are absent. The xylem vessels in the monocot stems are arranged in the form of the letter ‘Y’. The two
- metaxylem vessels are placed at the upper two arms and at base one or
- two protoxylem vessels are present. In a mature bundle, the lowest
- protoxylem break ups and forms a cavity known as protoxylem lacuna.
Describe stucture of dicot stem internally
- EpidermisThe young dicotyledonous stem shows that the epidermis is the outermost protective layer of the stem covered with a thin layer of cuticle; it
- may contain trichomes and a few stomata. The cells arranged in multiple layers between epidermis and pericycle constitutes the cortex. Epidermis
- cells are living and usually chloroplast are absent
- CortexIt lies below the epidermis and differentiated into three zones.Under the epidermis, there are minute layers of collenchymas cells called as hypodermis and main function to give mechanical strength to stem. Inner to the hypodermis, a few layers of chlorenchyma cells are present with intracellular space and it is the region of photosynthesis and the third zone contains parenchyma cells. The innermost layer of the cortex is
- called as endodermis and they are barrel in shape and compactly arranged without intercellular spaces.
- Stele It is located in the central part of the stem inner to the endodermis consists of pericycle, vascular bundles, and pitch. In dicot stem, the vascular bundles are arranged in a ring around the pitch. Pericycle
- occurs between the endodermis and vascular bundles. Vascular bundles contain xylem, phloem, and cambium. Xylem in the dicot stem consists of
- xylem parenchyma, xylem vessels, tracheids, and xylem fibres. Phloem
- consists of companion cells, sieve tubes, and parenchyma.
what are the factors effecting photosythesis
sunlight,water,co2,temperature ,leaf area
respiration is the process in which energy is realesed form cabohydrates to fuel growth in the plant
what is the formula for respiration
- cabohydrates + oxygen
- carbon dioxide +water+energy
Where does respiration take place in the plant
Respiration takes place in every living cell in the organelles known as the mitocondria
Describe how levels of oxygen and temperature affect respiration
- Temperature- The rate of respiration in a plant cell decreases when temperature decreases until respiration nearly or completely halts around freezing temperatures. Respiration increases with increasing temperatures until very high temperatures are reached and result in tissue deterioration.Temperature
- greatly affects respiration for maintenance (much more than cells dedicated to plant growth). Plants in temperate climates have much lower
- respiration rates in winter than during warm summers.The respiration rates of fruits can be controlled by storing fruit in cool,dry places. Lower storage temperatures are able to slow the respiration and ripening of fruit.
- OxygenRespiration decreases with decreased available oxygen. Under circumstances where no oxygen is present, like in poorly draining soil, anaerobic respiration (fermentation) occurs. Anaerobic respiration results in carbon dioxide, some energy, and ethanol. This type of respiration is also used to create alcohols. The rate of respiration for most plants peaks around the normal oxygen level in the atmosphere.
Transpiration – The loss of water from a plant and is caused by water evaporating inside a plant.
How do plants transport water and food
The phloem tubes
- Plants transport food and water around inside them using two
- different sets of tubing; xylem and phloem. They usually run along side each other and are called the leaf vein or vascular bundle
(or sieve tubes) are made up of living cells with a filters running through, and carries food from the leaves (where it is made) to everywhere else. They carry sugars, fats, proteins and other things like that to growing regions in shot and root tips, and to/from storage organs in the roots. They need a good supply of oxygen, otherwise they will die
- Xylem tubes (or vessels) are made of dead cells joined end to end. The walls of dead cells are stiff and contain lignin, which gives the plant support. They carry water and minerals from the roots to the leaves
- using the pressure of the transpiration stream and root pressure. Minerals are also transported with the water. In the roots, the xylem takes in water using root hairs to increase the surface area. The concentration of salt in the root hair is higher than in the soil, so
- water is drawn in by osmosis NB both extend down to the roots.
Define diffusion and osmosis
- Osmosis is the passage of water
- from a region of high water concentration through a
- semi-permeable membrane to a region of low water
– The passive movement of particles from an area of high concentration to an area of low concentration For photosynthesis to occur carbon dioxide must diffuse into the leaf (via the stomata) to the cells (especially the palisade cells). However, the oxygen and water vapour created by photosynthesis diffuses out of the leaf the same way,
What do plants do to prevent water loss
- Fewer stomata, the pores in the epidermis or skin of the leaf on the leaf can reduce water loss
- * In hot dry climates many plants open their stomata only in the cool of the evening.
- * Small leaves (totora, lavender) have a reduced surface area to enable plants to conserve water, as do feathery, filigree leaves
- (romneya, eschscholzia or Californian poppy).
- * Needle-like foliage (grasses, pine trees)
- has a very small surface area that looses very little water. Some of
- these plants can roll their leaves inwards, further reducing surface areas and water loss.
- * Leafless plants, such as brooms, have lost their leaves altogetherwith stems undertaking essential photosynthesis and food production.
- * Grey or light coloured foliage reflects light, reducing heat and thus water loss from transpiration
- * Thicker cuticles, the outer waxy coating on leaves, slows transpiration; many coastal plants have a thick glossy coating on the leaves, reducing water loss and also protecting from salt-burn.
- * Silver hairs coating leaves reflect light and help to lower temperatures inside the leaf, as well as reducing the effect of drying winds.
- * Thick fleshy leaves can store water; many succulents have thick leaves that, when bruised or broken, contain a great deal of moisture.
Describe the factors which effect transpiration.
Plants transpire more rapidly in the light than in the dark. This is largely because light stimulates the opening of the stomata (mechanism). Light also speeds up transpiration by warming the leaf.
- Temperature Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. At 30°C, a leaf may
- transpire three times as fast as it does at 20°C.
- HumidityThe rate of diffusion of any substance increases as the difference in concentration of the
- substances in the two regions increases.When the surrounding air is dry,diffusion of water out of the leaf goes on more rapidly.
When there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration. When a breeze is present, the humid air is carried away and replaced by drier air.
- Soil waterA plant cannot continue to transpire rapidly if its water loss is not made up by replacement from the soil. When absorption of water by the roots fails to keep up with the rate of transpiration, loss of turgor
- occurs, and the stomata close. This immediately reduces the rate of transpiration (as well as of photosynthesis). If the loss of turgor extends to the rest of the leaf and stem, the plant wilts.
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