Gas Exchange in Plants OCR Practical PDF

/.4 Gas exchan g e i n p l a n t s dl Green plants carry out photosynthesis to make their own food. v Flipped classroom During photosynthesis, they use carbon dioxide and produce oxygen Watch a vid...

/.4 Gas exchan g e i n p l a n t s dl Green plants carry out photosynthesis to make their own food. v Flipped classroom During photosynthesis, they use carbon dioxide and produce oxygen Watch a video They also carry out respiration to release the energy in food. During and answer respiration, they use oxygen and produce carbon dioxide. the questions. What gases do green plants take in and give out throughout the day? Let us study gas exchange” in plants in Practical 7.9 and 7.10. ® Practical 7. O Studying uptake or release of carbon dioxide | in plants Aim To find out the changes in carbon dioxide content in boiling tubes with green leaves under light and dark conditions Apparatus and materials per group | boiling tube 4 cotton thread | 2 pieces stopper 4 fresh green leaf ee 4 | test tube rack 1 aluminium foil | measuring cylinder (10 cm?) 1 hydrogencarbonate indicator table lamp 1 a | lower than normal level in air higher than normal level (about 0.04%) normal level hydrogencarbonate indicator red yellow 1 Add 3 cm’ of hydrogencarbonate indicator to each of four boiling tubes (A, B,C and D). Record the colour of the indicator in each tube. 2 Put two leaves into tubes A and C. Make sure the leaves do not touch the indicator. 3 Stopper the four tubes. Make sure there is no air leakage. TT ep prrrrrerpppppeppeeperrer yt PTI TT IT IY TITY PY PIRI PY TR TAT IPI VIR PRY RIAL LALZ SALADS ALIS LIAL 2 LAS 4 Latte (A Ey dididiittiitdiintttdnttdttttd YT ddd dL i tinttidiittbnad ILI LTA AA a ll II IEE ISSIR TI I TL TT  Gas exchange In plants 4 Wrap tubes C and D withaluminium foil. green leaves aluminium foil hydrogencarbonate indicator 5 Leave the four tubes in bright light for five hours. Record the colour of the indicator in each tube. Results Colour of hydrogencarbonate indicator At the beginning After five hours Discussion 1 What is the purpose of setting up tubes B and D? They are cortrdl, 4K Wha. They make sure the results in tubes A and C are caused by the presence of flo green boanes. ; 2 Compare the results of the following tubes. What can you tell about the gas exchange of leaves? a The indicator in tube A Twms purple. while the indicator in tube B rene red. This shows that under light conditions, the green leaves Take, IN carbon dioxide. b The indicator in tube C 1 WINS yell. while the indicator in tube D rAAUNL red. This shows that under dark conditions, the green leaves gl suk carbon dioxide. 41  Gas exchange In plants The net gas exchange in plants depends on the relative rates of photosynthesis and respiration. Under light conditions: Plants carry out both photosynthesis and respiration. The rate of photosynthesis is higher than the rate of respiration. Therefore, * the plants use more carbon dioxide in photosynthesis than they produce in respiration. As a result, there is a net uptake of carbon dioxide. the plants produce more oxygen in photosynthesis than they use in respiration. As a result, there is a net release of oxygen. A Lr el Fo Net at i BE 1 < ‘ uptake of Net release of carbon dioxide _ oxygen AEE WO SN hr A ‘ SOR]* Rag IY lyWE A Lia SAN a Tn’ vie “ es a P) : PNC (o}: /T i HE i i MP OL oy LE His = ) ox TA wy PP Vi ” ’ 4 VES ANYON —— Fig 7.17 Under light conditions, there is a net uptake of carbon dioxide and a net release of oxygen in plants Under dark conditions: Plants carry out respiration but not photosynthesis. Therefore, there is a net release of carbon dioxide and a net uptake of oxygen. Fig 7.18 Under dark conditions, there is a net release of carbon dioxide and a net uptake of oxygen in plants 45  “ Misconception (© } | X In green plants, photosynthesis occurs under A hE ~ light conditions and respiration occurs under ~ v/ Respiration occurs all the time in green plants. dark conditions. Ho Me Under light conditions, both photosynthesis and respiration occur in green plants. Key point e The net gas exchange in plants depends on the relative rates of _ photosynthesis ____ pivafion. and peg pr e Under light conditions, there is a net pplala. (uptake / release) of carbon dioxide and a net releases (uptake / release) of oxygen in plants. respiration e Under dark conditions, there is a net telease (uptake / release) of carbon dioxide and a net wpTake (uptake / release) of oxygen in plants. Gas exchange through stomata On the leaves of most plants, there are pores” called stomata”. They allow gases like carbon dioxide and oxygen to move into or out of the leaves (Fig 7.19). oxygen carbon dioxide Fig 7.19 Gases are exchanged through stomata on the leaf ARAL LL EL PPP PL LL Er PTT PPP EEE LEER EE ET PTT ER TEL EE senenn EA a4 pore Nf, stoma (pl. stomata) FFL  Gas exchange in plants Obse r v i n g s t o m a t a ® P f actical 7.11 Aim To observe stomata on the leaf epidermis under a microscope — —— — -— ——— Apparatus and materials per group light microscope 1 prepared slide of leaf epidermis 1 ——————————— 1 Observe a prepared slide of the leaf epidermis under a microscope at a low magnification (e.g. 100X). After seeing a clear image, observe the slide again at a high magnification (e.g. 400X). A Refer to Skill reminder on p. 192 for how to use a light microscope. 2 Draw a labelled diagram to show a stoma and the cells surrounding it. £3 ski tips When making a biological drawing of the specimen: e use a sharp HB pencil. e draw smooth, continuous lines. Do not sketch or shade your drawing. e draw different parts in proportion. e put labels on the sides using straight labelling lines. These lines must not Cross one another. write a title for your drawing. This should include the name of the specimen and the power of magnification. 45  iSectionfsummaryaz4: 1 The net gas exchange in plants depends on the relative rates of photosynthesis and respiration. 2 Gas exchange in plants under light and dark conditions: Conditions SEE Net oas exchange Light conditions Net uptake of carbon dioxide Rate of photosynthesis > rate of respiration * Net release of oxygen PASEO IE eee — = — FREE REN 3A etn CRU, 0 SU FORE SHER EW | | Dark conditions e Net uptake of oxygen | _ ne Respiration only e Net release of carbon dioxide - Sg eas a TI re Ln ae] @3 Gas exchange in plants is mainly carried out through the stomata. SectionlexerciseRZ IF 4; Questions 1 and 2: Write ‘T” for a true statement and ‘F’ for a false statement in the boxes provided. 1 Plants do not need to take in oxygen from the atmosphere. [a & D. 43 2 When the rate of respiration of a plant is higher than that of photosynthesis, there is a net release of carbon dioxide from the plant. [=] & p. 43 3 The photo on the right shows a potted plant near the window. a State the net uptake and release of gases of the leaves of the plant at noon in a warm sunny day. Explain your answer. (3 marks) : &p.43 @b In plants, gas exchange mainly occurs through a structure on the leaf epidermis. Name the structure. (1 mark) SToma. ep 4 46