Introduction
It is a common observation that organ and organ system level of organization is poorly developed in plants than animals. Although plants are more ancient but they are less developed because plants have to perform less range of activities and functions.However, processes like nutrition, gaseous exchange, transport, homeostasis, support, growth and development and movements in response to external and internal stimuli etc., occur in plants.
10.1 Nutrition in Plants
Plant nutrition is the study of chemical elements and compounds necessary for plant growth, plant metabolism and their external supply. A nutrient is a component in food that an organism uses to survive and grow. Almost all plants are autotrophs, i.e., they can manufacture their own organic compounds by obtaining inorganic nutrients such as water, CO, and certain minerals from environment.
A nutrient that is able to limit plant growth is considered as essential plant nutrient. There are 16 essential plant soil nutrients besides the three major elemental nutrients, i.e. carbon, hydrogen and oxygen. Plants must obtain these mineral nutrients from their growing medium.
Some of these minerals required in comparatively large amount are called macronutrients, e.g., nitrogen, phosphorous, sulfur, magnesium, iron, carbon, hydrogen, oxygen. Some mineral nutrients required in trace amount are called micronutrients, e.g., boron, chlorine, manganese, zinc, copper, molybdenum, cobalt, sodium. These elements are present in soil as salts which ionize in water so plants absorb them in the form of ions.
In the same soil again and again. The possible remedy for this problem fertilizers in soil and cultivation of different crops alternatively in the same! cultivation of legume plants along with normal crops.
10.1.1 Nutrition in Carnivorous Plants
Insectivorous or carnivorous plants are those types of plants that o their nutrients especially nitrogen by consuming insects or protozoans. Th adapted to grow in places where the soil is thin and poor in nutrients. The plants include the Venus fly trap, pitcher plants (Nepenthes), butterwe cobra lily and hundreds of others.
However, these plants do not deper insects and small animals for their nutrition. The main source of er autotrophic mode of nutrition like other plants. These plants trap inse animals just to fulfill their mineral nutrient deficiency." ese plants have s capture prey and enzymes to digest the prey.
10.2 Gaseous Exchange in Plants
Like animals, plants also need oxygen for cellular respiration and get rid of CO, produced during this process. This exchange of gases takes place by diffusion. In the daytime, leaves are photosynthesizing, so oxygen produced during photosynthesis is enough for respiration. At night oxygen diffuses into the leaves through the of stomata.
This oxygen dissolves in the thin layer of moisture around the cell and diffuses across the cell wall and cell membrane. The roots get their oxygen from the air space in the soil.
10.2.1 Role of Palisade and Spongy Mesophyll in Exchange of Gases
Most of the interior of the leaves between upper and lower side of epidermis contains parenchyma or chlorenchyma tissue called mesophyll (Greek for middle leaf). This tissue is the primary location of photosynthesis. The mesophyll is divided into two layers. An upper palisade layer of vertically donated cells one or two cells thick and obtain more chlorophyll and without spaces between them.
Beneath the palisade layer is a spongy layer. The cells of this spongy layer are not tightly packed so there are large intercellular spaces thus exchange of gases takes place more easily. These cells contain less chloroplast.
Types of mesophyll in dicot and monocot:
I cell layers are present, such leaves are called bifacial leaves. In monocot only spongy mesophyll layer is present between both upper and lower epidermis, such leaves are called monofacial leaves. The mesophyll cells are metabolically active cells due to photosynthetic process, therefore, these cells are rapidly involved in exchange of gases.
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