Photosynthesis
every organism needs nourishment to live;
nourishment is a source of substances essential for building up the body and the energy needed to carry out life processes;
organisms differ in the way they nourish – some are autotrophic, others are heterotrophic.
to explain what it means that photosynthesis is an autotrophic way of nutrition;
to determine the conditions affecting photosynthesis;
to conduct an experiment to illustrate the effect of light intensity on the intensity of photosynthesis;
to justify that photosynthesis is a key process for the existence of life on Earth.
Autotrophy of plants
The main substances used by plants to produce nourishment are two simple inorganic compounds: water and carbon dioxidecarbon dioxide. Land plants take water from the soil and carbon dioxide – from the air. These compounds produce simple sugar – glucose. The process of converting water and carbon dioxide into glucose takes place in the presence of light, which is why it is called photosynthesisphotosynthesis. The name of this process comes from the Greek words phos (light) and sýnthesē (creation).
Photosynthesis requires the green pigment – chlorophyllchlorophyll, which absorbs light, starting a series of chemical reactions. One of these is the decomposition of water into hydrogen and oxygen. Oxygen, as a by‑product, is excreted into the atmosphere, while hydrogen and carbon dioxide are used to produce sugars. The light energy is stored in the glucose molecules. All chemical reactions take place at the right rate thanks to specialised proteins – enzymes. The more intense the photosynthesis, the more organic substances the plants produce.
The substances needed for photosynthesis, i.e. its substratessubstrates, are water and carbon dioxide, and the products of this process are glucose and oxygen.
The rate of photosynthesis is influenced by both the external environmental conditions of plants and the elements of their internal structure. The intensity of this process depends on the amount and quality of light, the concentration of carbon dioxide in the air, the availability of water and mineral salts as well as the ambient temperature. Among the internal factors that determine the course of photosynthesis, the content of chlorophyll and enzymes is particularly important.
Carbon dioxide and water – substrates of photosynthesis
Carbon dioxide is the basic substrate of photosynthesis. Its concentration in the atmosphere is about 0.04%. The main source of this gas are the processes of decomposition of dead organic matter in the soil, carried out by bacteria and fungi. The amount of carbon dioxide in the air affects the intensity of photosynthesis – thus, an increase in its concentration leads to an increase in the mass of plants. However, the intensity of the process increases only up to a certain level of the plant’s saturation with this gas. Once this is achieved, a constant rate of photosynthesis is established, which depends on other factors, mainly on the rate of reaction carried out by the cellular enzymes.
How does the amount of carbon dioxide affect the rate of photosynthesis?
The more carbon dioxide there is in the water, the more intense the process of photosynthesis of Canadian pondweed will be.
3 glass beakers,
3 glass test tubes,
3 shoots of Canadian pondweed of equal length,
carbonated COIndeks dolny 22 tap water at room temperature,
still tap water at room temperature,
still boiled tap water at room temperature,
a lamp with a 100W light bulb used to light plants,
second hand or other timer.
Prepare and sign three experimental sets with different carbon dioxide contents: a beaker with carbonated tap water, a beaker with tap water, a beaker with boiled tap water.
Pour a suitable type of water into each of the three beakers and place in each of them a test tube filled with the same water and a branch of Canadian pondweed. Make sure that each branch has the same number of leaves. Turn the test tube upside down so that there is no air in it.
All sets must be placed at a distance of 30 cm from the light source.
The water temperature in each set should be the same.
After 20 minutes, start counting how many gas bubbles each plant emits in 5 minutes. The number of bubbles indicates the intensity of photosynthesis. Be sure to record the results accurately.
Repeat the experiment three to five times.
Record the results in the table and formulate a conclusion based on it.
If the number of bubbles counted within 5 minutes in a set with carbonated water differs significantly from the number of bubbles counted at the same time in a set with still tap water or still boiled tap water, we can conclude that the intensity of photosynthesis in the Canadian pondweed depends on the content of carbon dioxide in water.
Explain why in experiment 1. the rate of photosynthesis is measured by the rate at which gas bubbles are secreted.
After you watch the teachers experiment write down the research question and the hypothesis, observations and finally – conclusions.
Research sample is:
- a set with a plant put into still water
- a set with a plant put into carbonated water
- both sets
Water - besides carbon dioxide - is the basic substrate used by plants to produce glucose. The water content in the plant affects the opening and closing of stomata – holes in a leaf skin leading to the space between the cells filled with chloroplasts. Significant water scarcity causes closing of the stomata, inhibits the supply of carbon dioxide and reduces the intensity of photosynthesis. Plants which are deprived of water for a long period would wilt and fade.
Mineral salts
Together with water, a plant takes up the mineral salts necessary for its development. They are used to build organic compounds being part of the cells and regulate functioning of enzymes. The absence of mineral salts in the soil is a factor directly limiting photosynthesis. Nitrogen is necessary for building up of enzymes regulating this process. On the other hand, deficiency of magnesium, which is a component of chlorophyll, inhibits the synthesis of this pigment.
At the beginning of 18th century, Jan Baptista van Helmont conducted an experiment. He weighted the sapling of a willow tree and planted it in a pot with soil which was blanched and weighted beforehand. For 5 years, he was only watering the tree with rainwater. Once he weighted the tree again after that time, he found out that its weight increased to 75 kg, whereas the mass of the soil decreased by 53 grams. Why did 53 grams of the substance disappear from the pot where the willow planted by him grew for several years? What happened to it?
Products of photosynthesis
The main product of the photosynthesis processproduct of the photosynthesis process is glucose. This sugar, with the help of enzymes, is converted into other organic compounds such as starch, cellulose, fats and proteins, or is used as an energy source in the cellular respiration process. Plants use organic compounds, produced as a result of photosynthesis, to build cells and store energy. Excess of these substances is accumulated in roots, stems, leaves or seeds. When plants need glucose, they draw it from their reserves.
Oxygen is a by‑product of photosynthesis. During the day, plants produce much more oxygen than they need. Excess of this gas is released into the atmosphere through the stomata and used by plants and other organisms for breathing. Plants do not produce oxygen at night.
Conclusion
Photosynthesis is the process during which organic compounds and oxygen are formed from water and carbon dioxide – with the help of solar energy.
Organic substances produced during photosynthesis are nourishment for plants.
Oxygen from photosynthesis is used by plants and other organisms during respiration, and excess oxygen is released into the atmosphere.
Photosynthesis is carried out by organisms containing the green pigment – chlorophyll.
1. List the factors necessary for the photosynthesis process. Divide them into external – affecting the plant in its environment and internal – associated with the functioning of cells carrying out photosynthesis.
3. Plan an experiment to demonstrate that water is essential for the photosynthesis process.
Keywords
photosynthesis, substrates of photosynthesis, products of photosynthesis
Glossary
chlorofil – związek organiczny; zielony barwnik – główny składnik chloroplastów – umożliwiający wykorzystanie energii świetlnej w procesie fotosyntezy
chloroplast – składnik organellum komórki roślinnej i glonów (samożywnych protistów) zawierający chlorofil, w którym zachodzi proces fotosyntezy
dwutlenek węgla – gazowy związek węgla i tlenu; substrat fotosyntezy, produkt oddychania komórkowego
fotosynteza – proces syntetyzowania związków organicznych z dwutlenku węgla i wody, zachodzący w organizmach samożywnych pod wpływem światła, z udziałem chlorofilu i enzymów
produkty fotosyntezy – tlen i różne związki organiczne, w tym glukoza, które powstają w wyniku procesu fotosyntezy
substraty – substancje, które wejdą ze sobą w reakcję chemiczną
substraty fotosyntezy – woda i dwutlenek węgla; substancje chemiczne, które ulegają przemianie w trakcie procesu fotosyntezy