Topic: Fruit and seeds

Author: Elżbieta Szedzianis

Target group

Students of the 5th grade of an elementary school.

Core curriculum

5) Angiosperms. The student:

b) identifies the organs of an angiosperm and describes their external structure taking into account the functions of these organs (root, stem, leaf, flower, fruit).

The general aim of education

The students describe the structure and function of seeds and fruits, their adaptation to spreading, and the course and conditions of germination.

Criteria of success

• On the basis of observations, you will determine the type of fruit produced by peach, beans, peppers, oak, corn, beans,

• name five examples of fruit adapted to self‑spreading, by animals, wind,

• on the basis of observations and results of experiments, you will determine what germination is and on what factors it depends on.

Key competences

• communication in foreign languages;

• communication in the mother tongue;

• mathematical competence and basic competences in science and technology; 

• learning to learn.

Methods / techniques

Conversation, direct and replacement observation, work with text and film.

Individual work and work in groups.

Teaching aids

• abstract;

• interactive or traditional board;

• tablets/computers;

• collections of fruit;

• maple and sunflower fruit;

• wheat, sunflower seeds and pea seeds;

• 3 boxes of filter paper or a sheet of paper;

• 3 mortars with pestles;

• 3 test tubes;

• Lugola liquid;

• concentrated nitric acid (V);

• water.

Lesson plan overview (Process)

Introduction

1. The teacher asks the students to indicate fruits in the photograph from the Internet „fruits and vegetables isolated on a white background”. 

The teacher forms a key question: Can fruit be vegetables?

2. The teacher gives the topic, the goals of the lesson in a language understandable for the student, and the criteria of success.

Realization

1. The teacher asks the students to describe the structure of a fruit using the text entitled „Structure of a fruit”.

2. The teacher divides the students into groups. Each group receives a collection of seasonal fruit (or parts of fruit). The students have to divide them into groups and specify the criteria for division and indicate the common characteristic of the fruit.

3. The teacher displays the „Fruit types” diagram on the board and asks the students to check whether they have made such a division.

4. The teacher asks the students to discuss in a group and agree on how different types of fruit are spread, and indicate adaptations to such ways of spreading.

5. The teacher asks the students to redraw the diagram to the notebook and add examples of plants that produce such fruits.

6. The teacher asks the students to name similarities and differences in the structure of endospermic and non‑endospermic seeds (abstract: „Structure and types of seeds”), and then to open the sunflower and maple fruits and drew the embryo of one of the plants. The drawing should be made in accordance with the principles of the observation documentation drawing.

7. The students do interactive exercise No. 1.

8. The students perform Experiment 1, and write down the observations and conclusions in the notebooks.

9. The students do interactive exercise No. 2.

10. The students observe and describe wheat germination on a movie from the Internet titled „HD macro timelapse video of a grain seed growing and blossoming from the ground in soil, underground and overground view/Wheat plant growing from soil time lapse”.

11. The students read and discuss Experiment 2, and then they plan an experiment to confirm the hypothesis saying that „Light inhibits germination of cress”.

Summary

1. The students solve interactive tasks 3 and 4.

2. The students write down in their notebooks two notes entitled „Fruit functions” and „Seed functions”, then they read and compare them.

3. The teacher asks the students what they liked in the lesson most.

Homework for keen students.

Conduct an experiment that will allow checking the hypothesis saying that „Light inhibits germination of cress”. Take photos of the cultivation every day (photos will be a record of the observation). After 5 days, draw a conclusion and finish the cultivation.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Fruits and seeds

A fruit is the matured ovary enclosing the seeds. It is produced by angiosperms. Despite the fact that fruits take on different forms, each consists of the same parts: pericarp and seeds.

The process of fruit development begins after the fertilisation – a sperm cell and an egg cell coming together inside the ovule located in the ovary. After fertilisation, the ovule transforms into a seed, and the ovary wall into a triple layer pericarp. The outer layer is called exocarp, often fitted with different outgrowths – wings, hooks, hair. They facilitate transporting fruits by animals or wind. The middle layer is called mesocarp, it can be thick and fleshy like that of a peach, or thin and dry like that of a pea. The inner layer (endocarp) surrounds the seeds. It is woody in the case of drupes, leathery in the case of apples, and in the case of peas – membranous. The pericarp’s function is to protect seeds and facilitate their propagation. A fruit can contain one or many seeds.

Fruits display different adaptations for seeds propagation, reflected in their structure.

Singular fruits develop from a single ovary of a single flower. When they ripen, they can be fleshy or dry. Berries are fruits with the pericarp made of soft tissue, usually containing many seeds, like for example the watermelon. Drupes are fleshy fruits with a stone, represented by the cherry. Abundant edible flesh developed from receptacle growing around the ovary is a trait of accessory fruits like apple. In their case, the pericarp is a small part of the fruit, covering leathery seed cases. The pear and chokeberry are both examples of similarly structured fruits.

Majority of plants produces dry fruits with hardened pericarps. Dehiscent fruits are an example of those. When they ripen, they dry and open violently, launching seeds over long distances. They are divided into three categories: capsules (poppy), pods (bean) and siliques (rapeseed). Indehiscent dry fruits don’t open when they’re ripe. They have a hard and thick pericarp that cracks only when the seed sprouts. An example of those is the caryopsis – a type of fruit found in the wheat and corn, which develops as a result of the seed coat and thin pericarp fusing, making it look like a seed, and not like a fruit.
Similar to caryopsis, achenes have the pericarp and seed unfused, making it easy to separate them, for example in the case of the sunflower. On many achenes’ pericarps (thistle, dandelion) structures for seed propagation develop. A schizocarp (hollyhock fruit for example) contains many seeds. After ripening, it breaks down into mericarps. A completely hardened pericarp of a nut usually contains only a single seed. Fruits of the hazelnut tree, oak and buckwheat are nuts.

Seeds perform survival function. They adapted to stay dormant until conditions are right for sprouting. Annual plants stay dormant through the winter (in our climate) or the dry season, which is the only way for them to survive the wait for the right conditions. In the mature seed the processes of growth and development cease and the respiration is heavily slowed down. The dormancy can last from several days to many years. A typical seed consists of the embryo, the nutrition storage called endosperm, and the seed coat.

The hard and difficult to crack episperm protects the seed from drying, damage and pathogens. Many species develop all kinds of outgrowths facilitating propagation. Nutrition storage contained in the seed is barely used during the dormancy, when life processes are very slow. It is mainly used during sprouting, serving the embryo as an energy source during the growth and transformation into a seedling. In the beginning, the seedling uses the nutrition storage until it develops leaves and is able to photosynthesise.

Because of the origin of the nutrient tissue, we divide the seeds into endospermous and non‑endospermous seeds. The former have a small embryo surrounded by the big endosperm, like in cereals. The latter, like beans and sunflowers, have embryo filling the whole seed. In this case the endosperm was used during the embryo’s development, which resulted in creating large and thick cotyledons serving as storage organs.

The nutrients accumulated in the seeds vary. Depending on which substance dominates, we differentiate oilseeds, containing a lot of fat such as those of the sunflower and rapeseed, starchy seeds typical for cereals, and protein seeds such as the bean or pea.

Plants lack the ability to move. They can spread only thanks to fruits and seeds. The propagation can occur without any external help or via carriers such as wind, water and animals. In the case of some plants, it’s the whole fruit that gets propagated, in the case of others – it’s just the seed.

The self‑propagating of seeds is possible thanks to the inner forces acting on the fruit. Dry bean pods twist and explode, launching the seeds into the air violently. Capsules of the snapweed and violet fruits open up in a similar way: barely touched, they shoot their seeds several meters away. A plant called exploding cucumber squirts a stream of mucilaginous liquid containing its seeds.

The wind carries seeds and fruits adjusted to such method of locomation: lightweight and equipped for air travel. Maple and ash fruits have wings; dandelion and poplar fruits have pappus that increases their surface area.

Animals play an important part in transporting seeds and fruits, which can stick to their fur and feathers thanks to hooked outgrowths or spikes. Such catching devices can be found in burdock, cleavers and some species of sorrel. On the other hand, fleshy, juicy and colourful fruits make alluring food for animals. Inside their digestive tract, the pericarp is digested and the seeds get excreted unharmed with faeces. Humans in particular play a huge role in propagating fruits and seeds, consciously sowing plants in selected places and importing exotic decorative plants seeds from distant countries.

When the conditions in the environment are favourable, seeds start to germinate. During the first phase of germination they draw water intensely and puff up, gaining mass and increasing their volume. As a result, the seed coat cracks open. The radicle is the first to appear, going down into the soil. Soon the stem appears, and cotyledons with it. Once they’re in light, they become green and can begin to photosynthesise. The embryo slowly turns into a seedling. When the endosperm nutrition storage is all used up, the cotyledons wither and fall off.

During germination the seed wakes from the dormancy and life processes speed up inside the developing embryo. The presence of water is necessary for this process to commence. Water activates the enzymes that break down nutritious substances from the endosperm and cotyledons. The temperature of the environment is also important. Different plants seeds germinate in temperatures characteristic for the species, in the 0.5 – 40 °C range. Germinating seeds respire intensely, thus oxygen is also needed. Its deficiency or absence can be the cause of stopping the germination. In case of some plants, the process can be influenced by the light. It can both stimulate germination (lettuce) or inhibit it (cereals).

• Fruit is an organ typical of angiosperms only.

• Fruit protects the seeds and facilitates their spreading.

• Seeds have a survival function.

• Seeds contain the embryo of a new plant.

• Seeds and fruit have different adaptations to spreading.