22/10/15

It’s so sad to hear that today is our last lesson with Dr. Parameswari but luckily  we are still going to meet her due to the Scientist Trainee Programme. This week the lesson was on plant hormone. Plant hormones are chemicals that produced by plants to alter the growth pattern. We studied about five major plant hormones which are auxin, cytokinin, gibberellin, abscisic acid and ethylene.

During signal transduction in plant, hormone will bind to the receptor on the cell wall. Then molecules are relayed to the cell nucleus and response is given out. Generally, auxin induces growth in the shoot, root and stem of a plant but high concentration of auxin will inhibit the growth of root. Cytokinin promotes lateral bud growth and gibberellins breaks down seed dormancy. Abscisic acid promotes dormancy in seeds and bud while ethylene stimulates the ripening of fruit. The interaction between high ratio of auxin and low ratio of cytokinin promotes shoot growth while the opposite of it promotes root growth.

Plant is also sensitive to light and gravity. The shoot shows positive phototropism and negative gravitropism while the root is opposite to it. This is because when a plant is exposed to light, auxin moves to the sheltered part. Auxin stimulates faster cell growth and causes the shoot to bend toward light. However auxin is gathered at the lower part of the root due to gravity. This causes the suppression of root growth and the root will eventually bends downward.

In these 7 weeks, I have learnt about evolution, history of life, cell theory and prokaryote, endosymbiosis, pollination and development of plant embryo as well as plant hormones. There are some topics that I had learnt before and some I didn’t . However in overall, I gained a lot of knowledge and understood more on the topics. I believe that they would be very useful in the following studies as well as future prospect. I am glad to be Dr. Parameswari’s student because she never made the lessons boring as she carried out a lot of SCL activities which also helped us to understand more on the topics.

18/10/15

This week the lesson was on pollination and development of plant embryo. Although I have learnt this before but this is the topic that I am going to present for the Scientist Trainee Programme so I paid extra attention during the lesson.

The lecture refreshed my memory on the stages of plant undergoes to produce offspring. The male reproductive organ –stamen consists of anther and filament while the female reproductive organ-pistil consists of stigma, ovary and style. 

Each anther contains four pollen sac. The pollen mother cell undergoes meiosis to form tetrads of haploid microspores. The ovary undergoes meiosis to form ovule. Pollination occurs through pollinating agent like insect, wind and water. When pollen landed on stigma, pollen tube is stimulated to grow and transfer microspore to the ovary. Then double fertilisation occurs and seed is formed. This is the life cycle of angiosperm.

However, development of embryogenesis of plant includes the growth of zygote into basal cell and apical cell. Apical cell will grow into embryo while basal cell will grow into suspensor. They will then undergo globular stage, heart stage and torpedo stage to form seed. Dicotyledon has heart shape during heart stage and torpedo stage but monocotyledon does not have heart shape.

Throughout the lesson and SCL activities I have remembered how gametes and seeds are formed . With the knowledge I have I will try to teach the students in primary school in a simpler way and develop their interest in science.

11/10/15

This week the topic was on Endosymbiosis. Although I have learnt about mitochondria and chloroplast before, they were not as detail as mentioned in this topic. An American biologist proved that some organelles which are within cells were once free living cells. The examples given were mitochondria and chloroplast.

                                                                      Mitochondria

Endosymbiosis theory suggested that “Eukaryotes arose from a symbiotic relationship between various prokaryotes.”, “Heterotrophic bacteria became mitochondria while cyanobacteria became chloroplast.” and “The host cell of mitochondria as well as chloroplast was a large eukaryotic cell.”. I thought that the theories were true because the host cell couldn’t be smaller than mitochondria and chloroplast or else how did the host cell engulf the mitochondria and chloroplast.

                                                                   Cyanobacteria


Moreover,there are evidences that support the theories. For example, mitochondria and chloroplast have similar size and morphology as bacterial prokaryotic cells. Mitochondria and chloroplast are also divided by binary fission which are similar to bacteria and different to eukaryotes which divide through mitosis. They also have their own DNA and ribosomes with 30S and 50S subunits. They are also affected by antibiotics that used to kill bacterias. Anaerobic prokaryotes were formed 3.8 billion years ago while eukaryotes, mitochondria and chloroplast were formed 1.5 billion years ago. This showed the ancestor of mitochondria and chloroplast were prokaryotes because they need time to evolve from what they were to what they are now. Their ancestor couldn’t be eukaryotes as there wasn’t enough time for them to undergo evolution.

I think this topic is important to us because by the knowledge we gained in this topic we are able to differentiate whether a cell is from eukaryotes or prokaryotes. It could be very useful in the future when I’m doing research.

4/9/15

This week the lecture was on Cell Theory and Prokaryote. Before the lesson we were asked to look for the scientists who have contributed to cell theory. After doing research on internet, I had a brief idea on the discovery of cell. Robert Hooke, an English scientist and microscopist was the first person to discover cell. He observed a thin cutting of cork and discovered tiny boxes. He thought that the tiny boxes looked like cell and named it “Cell”. 

Anton Van Leeuwenhoek made his own microscope which can magnify object up to 250X and discovered bacteria and protozoa. He  named them “Animalcules”.

The scientist Theodore Schwann derived 2 theories which are “Cells are organisms and all organism consists of one or more cells.” and “Cell is the basic unit of life.”.

Rudolf Virchow was called The Father of Modern Pathology as he is the founder of social medicine and veterinary pathology. He also derived that “New cells come from pre-existing cells.” .

However, there are exceptional cases to the theories derived. We were asked “Is virus a living organism or non-living organism ?”. Initially my answer is yes and no because virus is in crystal form when it is in the air but it becomes active when it is in a cell. My thought was correct but virus is not considered as a living organism. This contributed to the addition of 4 theories which are “Cell contains hereditary information.” , “All cells are basically the same in chemical composition and metabolic activities”, “All basic chemical and physiological functions are carried out inside the cells. ” and “Cell activities depends on the activities of subcellular structures within the cell.”.

I never learnt about prion and viroid before. However I understood what they are after the lecture. Prion is an infectious protein that is misfolded. This causes the protein couldn’t function and aggregate. It remained in cell and attacked the nervous system as it cannot be degraded by protease. Viroid is a small RNA that consists of 250 nucleotides. It is not coated with protein and will only affect plants. It causes distorted shape in plants.

                                                                                         Potato tubers infected by viroid. 

Although I have learnt prokaryotes, eukaryotes and viruses before but cell theory, prion and viroid are new to me. So in the end f the lessons I still gain a lot of knowledge which makes me feel that I’m improving and getting smarter everyday.