1 letter:
.

3 letters:
dna, rbc, rna, rod

4 letters:
axon, clon, cone, hold, keep, mrna, nrna, oken, ovum, scnt, tank, trna

5 letters:
anode, aster, axone, clone, eosin, kinin, linin, ovule, panic, pilus, sperm, spots, woody, zonal

6 letters:
cancer, chitin, cilial, cilium, citrin, colony, coltan, cooler, crenel, diatom, folate, gamete, htlv-1, karyon, lignin, mature, miosis, neuron, pitted, reagin, turgor, velban, virino, wilmut, zygote

7 letters:
agonist, auxesis, bedless, bullpen, cambium, cathode, ciliary, ciliate, cloning, diploid, dungeon, eccrine, fission, floater, folacin, galvani, haploid, histone, meiosis, mitosis, nuclear, nucleus, scallop, schwann, spindle, trisomy, vacuole

8 letters:
acaryote, acrosome, akaryote, amitosis, amitotic, apocrine, cavitied, cd4 cell, cd8 cell, crenelle, cyclosis, dendrite, dry cell, egg cell, facility, galvanic, ganglion, hydremia, lysozyme, nucleole, okenfuss, pycnosis, pyknosis, ribosome, rod cell, sweatbox, tracheid, triploid, wet cell

9 letters:
al-tawhid, alveolate, al tawhid, anaplasia, apoptosis, astrocyte, beta cell, bone cell, bromeosin, cell-free, cell-like, cell wall, centriole, chromatin, cone cell, crenation, crenature, cytokinin, cytolytic, cytoplasm, cytoplast, endoplasm, endospore, enucleate, exudation, faveolate, fuel cell, guardroom, hair cell, haploidic, hybridoma, inclusion, karyotype, kerr cell, labrocyte, lignified, macrocyte, mastocyte, mast cell, merozoite, microcyte, monoploid, mosaicism, nucleolus, organelle, osteocyte, phagocyte, polyploid, replicate, root hair, schleiden, secretion, secretory, stainable, stem cell, streaming, syncytium, transform, transport, vacuolate, vitamin m, vitamin p

10 letters:
acanthosis, achromatin, akaryocyte, ameloblast, apposition, archespore, blastocyte, blastomere, brain cell, catenulate, cd4 t cell, cd8 t cell, cell organ, cell phone, chemotaxis, chromosome, clark cell, clostridia, eubacteria, fibroblast, folic acid, gametocyte, glial cell, homunculus, hyaloplasm, ian wilmut, karyolymph, karyolysis, karyoplasm, leucopenia, leukopenia, lymphocyte, lymphokine, lymph cell, megalocyte, melanocyte, metabolism, metastasis, microscope, muramidase, mycoplasma, nerve cell, neuroblast, one-celled, osteoblast, osteoclast, parenchyma, parthenote, plasmacyte, polar body, protoplasm, siderocyte, solar cell, sperm cell, spherocyte, taste cell, vacuolated, vitamin bc

11 letters:
acanthocyte, cancer cell, chlorophyta, chromatinic, ciliophoran, clostridium, cytokinesis, cytokinetic, erythrocyte, eubacterium, gametangium, goblet cell, gray matter, grey matter, helper cell, heteroploid, honeycombed, killer cell, leydig cell, lorenz oken, megaloblast, melanoblast, mother cell, muscle cell, myonecrosis, nerve fiber, nerve fibre, nuclear rna, nucleoplasm, plasmablast, plasma cell, replication, retinal rod, sickle cell, soluble rna, superinfect, target cell, totipotence, totipotency, tumor virus, unicellular, vinblastine, weston cell

12 letters:
acantholysis, acceptor rna, achromatinic, amphidiploid, archesporium, bioflavinoid, cadmium cell, cell nucleus, cytomembrane, cytoskeleton, divine unity, erythroblast, hypobasidium, karyokinesis, karyokinetic, mercury cell, muscle fiber, muscle fibre, preformation, prickle cell, primary cell, radical cell, reticulocyte, retinal cone, schwann cell, sleeper cell, somatic cell, spermatozoan, spermatozoon, stainability, storage cell, template rna, transduction, transfer rna, transudation, voltaic cell

13 letters:
beta receptor, cell division, cell membrane, coccobacillus, columnar cell, cuboidal cell, daughter cell, endomycetales, extracellular, galvanic cell, growth factor, helper t cell, intracellular, killer t cell, leydig's cell, luigi galvani, megakaryocyte, messenger rna, microgliacyte, neurogliacyte, purkinje cell, selenium cell, single-celled, squamous cell, standard cell, true bacteria

14 letters:
alpha receptor, autoregulation, auxiliary cell, cytophotometer, cytophotometry, detention cell, embryonic cell, formative cell, gray substance, grey substance, gustatory cell, leclanche cell, musca volitans, red blood cell, scavenger cell, secondary cell, terrorist cell, transformation

15 letters:
calcium blocker, differentiation, fertilized ovum, intussusception, leptosporangium, lorenz okenfuss, m. j. schleiden, neoplastic cell, neuroglial cell, oligodendrocyte, plasma membrane, theodor schwann, vegetative cell

16 letters:
action potential, active transport, cytotoxic t cell, detention centre, flagellated cell, ground substance, leptosporangiate, living substance, myenteric plexus, operational cell, ribonucleic acid

17 letters:
beta-adrenoceptor, bone-forming cell, cellular division, chromatin granule, correlation table, electrolytic cell, informational rna, intelligence cell, lead-acid battery, metabolic process, muscae volitantes, passive transport, photovoltaic cell, resting potential, spore mother cell, substantia grisea

18 letters:
alpha-adrenoceptor, ciliated protozoan, matthias schleiden, oat cell carcinoma, plexus myentericus, reduction division, second-hand speech

19 letters:
clark standard cell, columbite-tantalite, intracellular fluid, isles of langerhans, nickel-iron battery, order endomycetales

20 letters:
division chlorophyta, islets of langerhans, pteroylglutamic acid, respiratory quotient, small cell carcinoma, striated muscle cell

21 letters:
deoxyribonucleic acid, islands of langerhans, lead-acid accumulator, programmed cell death, striated muscle fiber

22 letters:
desoxyribonucleic acid, semipermeable membrane, theory of preformation

23 letters:
calcium-channel blocker, nickel-iron accumulator, nuclear transplantation

24 letters:
beta-adrenergic receptor, columnar epithelial cell, cuboidal epithelial cell, pteroylmonoglutamic acid

25 letters:
alpha-adrenergic receptor, oxidative phosphorylation

27 letters:
caspase-mediated cell death

28 letters:
malignant neoplastic disease

29 letters:
human t-cell leukemia virus-1, somatic cell nuclear transfer

36 letters:
somatic cell nuclear transplantation