Biology-Mr.Willets
Lab-Flowers
The most complex type of plants are called angiosperms (flowering plants). There are two major groups within the angiosperms- monocots and dicots. Some of the differences between them will be mentioned today. Other differences will be discussed in class and future labs. Daffodils are monocots.
The flower is the reproductive part of angiosperms . Some flowers produce only pollen (which contains the sperm), some flowers produce only eggs but most flowers (like the daffodil) produce both kinds of gametes.
Examine the daffodil. You will notice that outside the petals there are a few dried leaf-like structures. They are called the sepals. They protected the flower when it was just a bud. Notice the veins in the sepals. The veins are parallel to each other. This is a characteristic of monocot leaves (See question #1a)
Inside the sepals are the petals. All the petals together are called the corolla. The petals of the daffodil are brightly colored. This flower is designed to attract bees for pollination. (see question #2) Notice how far down inside the flower the inner structures are located. Remember this for question #3.
Carefully remove the petals without damaging the inner structures. How many individual petals were present?______ (*Flowers of monocots typically have flower parts in multiples of three. Dicot flowers have them in groups of 4 or 5. See question #1b) There is one large circular petal-like structure. Remove as much of this as is needed to better see the internal structures of the flower.
There is one structure in the middle of the flower which is usually taller than the rest. This is the female part of the flower. It is called the pistil. At the very top of the pistil is a sticky part called the stigma. Pollen sticks to this. The long tube that leads to the bottom of the pistil is called the style. The very bottom of the pistil is the ovary where the eggs cells are located. In daffodils, this part is the bulge seen just below where the petals were attached.
The structures that surround the pistil are the stamens. These are the male parts of the flower. These are usually shorter than the pistil. The very top of the stamen is the anther where the pollen is produced. How many stamens are there in your flower? _________ *Refer back to the information about monocot/dicot flower differences. (See question #1c) Are the tops of the stamens near the top of the flower? Would the wind be likely to blow pollen out of the flower with the stamens in this position? (see question #3)
Consider which is taller: the stamens or the pistil (assume it is the pistil).
If an insect went into this flower and buzzed around near the bottom where the nectar is, would it most likely:
A) cause pollen to fall from the anther onto the stigma (top of the pistil) OR B) cause pollen to fall on to the insect which would carry it to the next flower. If the stamens are below the top of the pistil, the flower would most likely _____________ (self or cross) pollinate? (see question #4)
Bring your flower to the front of the room. Place a drop of water on a slide. Place one anther in the water. Some pollen should now be in the water. Remove the anther, add a cover glass and examine using low power. (See question # 5).
When the pollen lands on the stigma, it starts to grow a pollen tube down the style until it reaches the egg cells. At the end of the pollen tube is the sperm with a half set of chromosomes. Then fertilization occurs and the zygote grows into a seed. The ovary thickens and becomes the fruit. The number of seeds depends on the number of egg cells fertilized. Cut into the bulge located just below the petals. This is the ovary where the seeds would develop.
In some plants. the long thin pollen tubes remain after fertilization. These can be seen in ears of corn before it is cleaned for cooking. (See question # 6) Each kernel of corn is a seed. If the ear of corn has some very small kernels, these were egg cells that were not fertilized and therefore did not fully develop.
Questions-
1)What 3 characteristics of this flower indicate that it is a monocot?
a) ______________________________________________________
b)______________________________________________________
c)______________________________________________________
2) What characteristic of a daffodil tells you it is insect pollinated?______________________________
3) What characteristic of the stamens tells you that daffodils are not wind pollinated?_________________
_____________________________________________________________________________
4)Why would it be difficult for this flower to self-pollinate? .________________________________ _____________________________________________________________________________
If a flower self-pollinates, the top of the stamens are generally located _________________ the pistil.
5) Describe the pollen grains and make a simple diagram.
6) What part of an ear of corn are the pollen tubes?_________________________________________
7) What is the female part of a flower called? ________________ What are its three parts?
___________________________________________________________________________
8) What is the male part of a flower called? ___________________What part of this actually produces the pollen? __________________
9) Use the book (pg 375) to help make a simplified diagram of a flower as seen from the side with some petals removed. Label petals, pistil and stamen. Make a separate diagram of a stamen-label the anther. Make a separate diagram (see pg 379) of a pistil- label stigma, style and ovary.