Cell Biology and Structure

• The nuclear membrane or karyotheca is a double membrane having pores at intervals.
• The nuclear membrane on its inside has a supporting membrane called the nuclear lamina or the fibrous lamina having a uniform thickness.
• It is a dense network of fibres present inside the nucleus of cells and are made up of intermediate filaments and membrane-associated proteins.
• It provides mechanical support to the nucleus and also regulates DNA replication and cell division 
• So, the correct answer is 'Both B and C.'

• A nucleus is a membrane-bound organelle containing the genetic material in the form of DNA molecule coiled to form the chromosomes.
  
• The nuclear membrane or the nuclear envelope is a lipid bilayer membrane (porous double-membrane) that encloses the nucleus.
  
• Nuclear membranes have protein-based channels known as nuclear pores which allow the transport of molecules across the nuclear envelope.
• So, the correct answer is 'Porous double membrane'.

• The DNA present in the nucleus undergoes transcription to form the messenger RNA or mRNA.
  
• The mRNA formed within the nucleus is transported out of the nucleus and into the cytoplasm of the cell and gets attached to the ribosomes. 
• It then synthesis proteins in the cytoplasm which is required by the cell for various cellular activities.
• So, the correct answer is 'RNAs'.

• Messenger RNA is formed in the nucleus.
  
• The process by which mRNA is formed from the DNA present in the nucleus is called transcription.
• The mRNA formed within the nucleus is transported out of the nucleus and into the cytoplasm of the cell and gets attached to the ribosomes. 
• It then synthesis proteins in the cytoplasm which is required by the cell for various cellular activities.
  
• So, the correct answer is 'Nucleus'.

• The mitochondria is a double-membraned cell organelle, known as the powerhouse of the cell which is present in all eukaryotic cells.
  
• The nucleus is enclosed by the nuclear envelope which is a double-layered membrane that consists of nuclear pores to regulate the transportation of substances such as RNA into and out of the nucleus. 
• The chloroplast is also covered by a double membrane which is known as the chloroplast envelope.
• So, the correct answer is 'Mitochondria, nucleus and chloroplast'.

The nucleus contains a viscous liquid called nucleoplasm. It contains chromosomes and nuclei. It is surrounded by a nuclear membrane and it helps in the exchange of material between nucleus and cytoplasm. So, the correct answer is option B.

Neuron carries signals between the brain and various parts of the body. The chloroplast is a type of plastid, which produces green coloured pigment. The chloroplast is involved in carrying out photosynthesis. It gives a green colour to leaves. Mitochondria produce the energy currency, i.e., ATPs of the cell. It is also called as a powerhouse of the cell as it provides energy currency to a cell. 

DNA is a long polynucleotide strand, coiled to make chromatin fibres to fit into the cell. It also helps to prevent DNA damage. It is situated in the nucleus. 

There are three major functional parts of the cell such as plasma membrane, cytoplasm and nucleus. Plasma membrane regulates the particles entering or leaving the cell. It carries out endocytosis, exocytosis and transport of various substances through different carrier proteins. It is also involved in cell signaling. 
Cytoplasm is a gel-like substance present in all cells. All of the cell organelles are suspended in the cytoplasm. Most of the cellular activities as metabolic pathways like glycolysis, key processes like cell division occur in the cytoplasm. Nucleus regulates all the cellular activities by controlling the enzymes required for cellular processes. The four main cellular functions of the cell are protein synthesis, cell division, growth and differentiation are carried out by the nucleus. 

So, the correct answer is option A.

Sieve tubes are cells of phloem found in certain plants and help in long distance translocation and distribution. Their nucleus is fragmented and disappeared. Mammalian erythrocytes also called as red blood cells are formed in bone marrow from multipotential hemocytoblast and further converted to erythroblast (normoblast). The nucleus and mitochondria of erythroblast disappear and it is converted to mature erythrocyte with haemoglobin. Erythrocytes cannot multiply as they lack the nucleus and can survive for 100-120 days. Monocytes are immune cells of the human body and are capable of dividing into macrophages. So they have the well-defined nucleus. So nucleus is absent in sieve tube cells and mammalian erythrocytes.

The nucleus is membrane-bound organelles which are seen under a light microscope because of its large size. These are spherical in shape and encompasses nuclear membrane, chromosomes, nucleoplasm and nucleolus. It contains the cell's genetic material.

The nuclear envelope is a membrane barrier that separates the nucleus from the cytoplasmic in eukaryotic cells. It contains a large number of proteins. The nuclear envelope is composed of two concentric bilayer membranes. The two layers are fused together into numerous tiny holes called the nuclear pores.