Лабораторная работа

Биология и генетика

Theoreticl informtion Photosynthesis converts light energy into the chemicl energy of sugrs nd other orgnic compounds. Light energy from light drives the rections. Photosynthesis uses light energy to drive the electrons from wter to their more energetic sttes in the sugr products thus converting solr energy into chemicl energy. The solr energy clled visible light drives photosynthesis.



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Done by T. Shchetynska, IACS 405

Laboratory work #2


Aim: to research the process of photosynthesis.

Theoretical information

Photosynthesis converts light energy into the chemical energy of sugars and other organic compounds. This process consists of a series of chemical reactions that require carbon dioxide (CO2) and water (H2O) and store chemical energy in the form of sugar. Light energy from light drives the reactions. Oxygen (O2) is a byproduct of photosynthesis and is released into the atmosphere. The following equation summarizes photosynthesis:

6CO2 + 6H2O → 6(CH2O) + 6O2

Photosynthesis transfers electrons from water to energy-poor CO2 molecules, forming energy-rich sugar molecules. This electron transfer is an example of an oxidation-reduction process: the water is oxidized (loses electrons) and the CO2 is reduced (gains electrons). Photosynthesis uses light energy to drive the electrons from water to their more energetic states in the sugar products, thus converting solar energy into chemical energy.

The solar energy called visible light drives photosynthesis. Solar radiation is composed of electromagnetic energy that travels through space in a manner analogous to the motion of waves in water. The distance between the crests of waves is called the wavelength. The shorter the wavelength, the greater the energy for each unit (photon) of electromagnetic energy.

Leaves are a plant's main photosynthetic organs. Leaf structure is closely associated with its photosynthetic function. Leaves must permit carbon dioxide access to the photosynthetic cells but impede water from diffusing out. The oxygen that is a waste product of photosynthesis must be allowed to escape from the leaf.

Mesophyll cells are specialized for photosynthesis. These cells in the middle of the leaf contain many chloroplasts, the organelles that perform photosynthesis. The gas exchange (oxygen and carbon dioxide) takes place within the chloroplasts, and the food produced by the chloroplasts must move out of the cells to other parts of the plant.

Chloroplasts are the sites of photosynthesis. These double-membrane bound organelles enclose additional membranes called thylakoids. The disc-shaped thylakoids possess an interior space. The thylakoids are stacked to form grana, which are suspended in the stroma of the chloroplasts.

There are three main factors affecting photosynthesis and several corollary factors. The three main are:

  1.  Light irradiance and wavelength
  2.  Carbon dioxide concentration
  3.  Temperature.


In the abstract sense a microscope is a device which records the interaction of a probe of some sort with the object. The probe may be a some form of radiation or even a pointed tip. Different forms of microscopy utilize a variety of physical principles - light microscopy utilizes the the interactions of photons with the specimen, electron microscopy utilizes the interaction of electrons with the specimen and scanning probe microscopy utilizes a variety of different interactions of a fine tip with the specimen.

The most widely used microscope uses light to create images of light transmitting specimens which are projected onto either the eye or a camera. The key components are a light source, an optical system, a specimen holder and a recording medium.

The purpose of the optical system is to collect the those photons that have interacted with the specimen and form them into an image. In the case of light this is done by means of lenses, shaped from light transmitting materials. A large number of materials are transparent to photons in the visible part of the electomagnetic spectrum - this makes the fabrication of microscopes using visible light simple and cheap. The process of image formation for other types of radiation is not so simple and what is achieved by a lens in the case of light needs to be achieved in other ways.

Using a Microscope

  1.  Put the microscope near a window or put a light source in front of the microscope.
  2.  Adjust the mirror to reflect light on the stage.
  3.  Put the specimen on a clean slide and put the slide on the stage.
  4.  Choose an eyepiece and an objective suitable for studying the specimen.
  5.  Watch the microscope from the side and carefully lower the objective by turning the coarse adjustment until it is just above the slide.
  6.  Now look down the eyepiece. Try to keep the unused eye open. Turn the coarse adjustment knob in the opposite direction so that the objective is raised. Stop turning until you see the specimen clearly.
  7.  Adjust the fine adjustment knob until the specimen is in sharp focus.

Safety Information

  1.  When carrying the microscope from one place to another, you should hold its arm with one hand and the base with your other hand.
  2.  When lowering the objective by turning the coarse adjustment knob, be careful not to bring it too low until it touches the slide.
  3.  When changing a slide to be observed, move the objective away from the slide first.

Laboratory procedure

During this experiment rowan leaves are researched. In the first case, the leave is alive, its colour is green. The second one, the leave is dried (dead), its colour is yellow. By means of the microscope we obtain such results:


So the main conception of the photosynthesis is the conversion of electromagnetic energy of light into the chemical energy. The green colour of the leaves, in our experiment, is conditioned by the absorption of red and violet beams of solar spectrum. During autumn or winter season plants “go into hibernation” and their leaves die in such way, they change their pigmentation. In such condition the roots of plant dry out and can not supply the water to the leaves.


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