The Association for Science Education

K2.3 Green plants and organisms

Abstract

The article provides an outline of the expectations of the National Curriculum regarding green plants at Key Stages 1 - 4 and explores the various alternative conceptions held by learners. Photosynthesis and respiration are dealt with in some detail and useful downloads are provided to assist with learning about plants. A range of practical ideas for use with trainees and in school is provided.

This is one of 17articles on www.scitutors.org.uk/ whose main aim is to support the processes of teaching/learning between the science education tutor and the trainee science teachers with a focus on “teachers’ knowledge and understanding”. During a primary or secondary BEd, PGCE or GTP we hope that those learning to become science teachers will be able to challenge their own understanding of science and scientific concepts. Unit K0 specifically explores general issues relating to all the knowledge units - to the learning of science.

Standards: This unit specifically addresses Q14 but, appropriately used can contribute to and provide evidence of competence for many others of the standards especially Q4,6,7,8,18, 22 and 25.

Key words: Green plants, living things, photosynthesis, respiration.

Contents

1.0 Introduction
2.0 The conceptual barriers to understanding
3.0 Progression in children's ideas
4.0 Giving Practical experiences
5.0 Useful References

1.0 Introduction

A few primary teachers will have completed some post 16 study or even have a degree in biology, and about half of the secondary science teachers will have a degree with some biology content. However, that means that a substantial number of trainee teachers of both primary and secondary phases will have an understanding of Biology equivalent only to a grade C at GCSE. The aim of these five ‘biology’ units is to provide support for these trainees (via their tutors) so that they can either teach to GCSE level, or acquire an understanding at that level so they have the confidence to teach at primary school. The emphasis is on the conceptual changes needed by learners (tutors, teachers and their pupils) to come to an understanding of living things.

Green plants as organisms

The National Curriculum for England has spelt out in some detail what should be taught:

At KS1

  1. to recognise that plants need light and water to grow
  2. to recognise and name the leaf, flower, stem and root of flowering plants
  3. Life cycle of plants 1 - that seeds grow into flowering plants.

At KS 2:

  1. the effect of light, air, water and temperature on plant growth
  2. the role of the leaf in producing new material for growth
  3. that the root anchors the plant, and that water and minerals are taken in through the root and transported through the stem to other parts of the plant
  4. Life cycle of the plants 2 - the various stages of the plant life cycle: germination, growth and development, reproduction (emphasises the need to leave germination experiments until KS2 - this is too often carried out at KS1 i.e. cress experiment where the emphasis is on growth and too often they begin with the seed and not the seedling)

At KS3

  1. that plants need carbon dioxide, water and light for photosynthesis, and produce biomass and oxygen
  2. to summarise photosynthesis in a word equation
  3. that nitrogen and other elements, in addition to carbon, oxygen and hydrogen, are required for plant growth
  4. the role of root hairs in absorbing water and minerals from the soil
  5. that plants carry out aerobic respiration.

At KS4

  1. the reactants in, and products of, photosynthesis
  2. that the rate of photosynthesis may be limited by light intensity, carbon dioxide concentration or temperature
  3. how the products of photosynthesis are utilised by the plant
  4. the importance to healthy plant growth of the uptake and utilisation of mineral salts
  5. the hormonal control of plant growth and development, including commercial applications
  6. how plants take up water and transpire
  7. the importance of water in the support of plant tissuesthat substances required for growth and reproduction are transported within plants.

2.0 The conceptual barriers to understanding

(Download 2.0a) Questions about plants can be used to elicit students' pre-existing ideas about how plants work. This deals with a number of confusions, such as the distinction between germination and growth, and whether plants respire at all or only some of the time. The accompanying PowerPoint (download 2.0b) can be used with intending teachers to get them thinking about how plants work and to address some of their misconceptions. It will also help those that do have good biological knowledge to see the problems that face those, such as their pupils in school, who are trying to understand plant biology.

The video ‘Simple Minds' is well worth showing to trainee teachers. It shows interviews with MIT science graduates about where they think the ‘stuff' that wood is made of come from. Many rely "The dirt, the soil". The students express surprise when the interviewer suggests that it comes from carbon dioxide in the air. This question is asked in the PowerPoint in download 2.2, and is a good starting point to help trainee teacher with their subject knowledge.

Download K2.3_2.0a 'Questions about Plants'
Download K2.3_2.0b 'PowerPoint: Green Plants and Organisms' 
[Note, in order to play the video of the bean germinating (on slide 18), you need to download and save the video file bean.avi (below in Download K2.3_3.0a) in the same folder as the PowerPoint.]

3.0 Progression in children's ideas

The National Curriculum programme of study, listed in the introduction, doesn’t identify any of the barriers children may face when trying to understand what plants are and how they work.

For example, the KS1 topics already assume that children realise that plants are alive - they are a life-form. Showing young children time lapse photographic sequences (for example the germinating bean in download 3) is very good evidence for movement and growth, which normally cannot be seen except in some of the touch sensitive plants. Even then plants don’t eat, do they? They can’t see can they? We need to help intending teachers to address these questions with the pupils they teach.

Early experiences with germinating seeds and growing them on into plants will help show children the life cycle of plants. If they can collect seeds and sow them, this will emphasise this cycle.

When asked to name some plants children often stick to either bright large flowers or houseplants. If, by plant, we refer to producers* at the start of food webs, we must ensure that our pupils also have the same broad view: trees, cabbages, grass, daffodils, all are plants. [*Remember that not all food chains begin with true plants, therefore not all producers are true plants i.e. phytoplankton & Pleurococcus (single celled photosynthesising organisms)]

Children are less aware of the names of plant groups than of animal groups. Nature walks where they identify common wild flowers and trees are so helpful in helping them realise that not all trees are the same and not all hedgerow and grassland plants are the same.

Once children learn about photosynthesis and they hear that this is in ‘contrast’ to respiration, many believe that plants only respire during the night, because they give out oxygen and take in carbon dioxide in the daytime. Whether a plant takes up or gives out carbon dioxide depends on how much light there is. The arrows in the following diagram show the movement of carbon dioxide into and out of a tree:

day (full light)
Photosynthesis is faster than respiration. The plant takes  in much more carbon dioxide than it gives out (if any at all).



dawn and dusk (dim light)
Photosynthesis and respiration proceed at the same rate. The plant takes in the same amount of carbon dioxide as it gives out.
 

night (dark)
Photosynthesis stops, respiration continues. The plant gives out carbon dioxide but no longer takes it in.

But this is not the full picture; every cell in a plant has to respire, even those with chlorophyll. Those parts of a plant that have no chlorophyll, such as a germinating seed or the roots, have to get all their oxygen from the air. Aquatic plants normally obtain sufficient from the oxygen dissolved in the water. See slide 22 of download 2.0b showing a mangrove plant which sends up ‘snorkels’ from its roots to enable them to obtain oxygen for respiration - their roots are often submerged in water, which has very low oxygen levels.

Download K2.3_3.0a 'Time lapse of germinating bean'

4.0 Giving Practical experiences

Download 4 Ideas for schools has some suggestions for intending primary teachers for activities suitable for use in school. Some of these are worth doing with the trainee teachers in college sessions to give them a flavour of the school activities. Although practical work is important in school it is probably more important that intending teachers think about what they hope their pupils will learn from the practical work they do, rather than simply carrying it out themselves. After all most of them have had the experiences, but they are unlikely to have thought about the way children’s ideas can be challenged the practical work they do.

Secondary school intending teachers will have plenty of opportunity in school to observe and try out the various practical experiences pupils in school will have, so once again the important thing in ‘college’ sessions is to allow them to reflect on what purpose the practical work serves.

Download K2.3_4.0a 'Ideas for school'

5.0 Useful References

This unit used, as a major resource, the CDrom (Ross at al 2005) with support from the associated book (Littledyke, Lakin and Ross, 2000) and the course guide (Littledyke et al., 2006).

Section Developed by:
Keith Ross, University of GloucestershireSeptember 2006

Published: 13 Sep 2006, Last Updated: 13 Sep 2008